cost: three months priced, from the module's defaults and the lists the AWS pricing page loads

README.md

@@ -64,6 +64,11 @@ that is not one task (`go tool taskgate`).
   characters (it is its line in `llms.txt`), every `SPIN_` variable a page names is one spin's
   `hack/env-catalog.txt` lists, and the table of states in `concepts/workspaces.md` is the API's
   `WorkspaceState`, both ways. `task reference:check` fails on each.
+- **The cost page's numbers are generated and dated**: `task pricing` (`tools/pricing`) writes
+  `src/data/pricing.json` - the machines the module starts by default, priced on demand in each
+  region with images, from the lists the AWS pricing page loads - and `task reference:check`
+  fails on a record a month old or of other machines than the module's defaults at its pin. The
+  daily sync rewrites it.
 - **What the site documents** is `src/data/reference.json`, written by `task reference`. Two
   things it keeps apart: the spin release an installation runs (`spin.installs`, the newest
   release `images.json` has images of), and the spin commit the reference is generated from

Taskfile.yml

@@ -31,9 +31,18 @@ tasks:
       - go run ./tools/sources spin spin-terraform-aws brand
 
   sources:bump:
-    desc: Move the pins to the newest releases - spin only to one that holds the commit pinned, brand to its main - and fetch them. Then task reference.
+    desc: Move the pins to the newest releases - spin only to one that holds the commit pinned, brand to its main - and fetch them, and rewrite the prices. Then task reference.
     cmds:
       - go run ./tools/sources -bump spin spin-terraform-aws brand
+      - task: pricing
+
+  # The cost page's numbers: generated, dated, and refused by reference:check once they are a
+  # month old or of other machines than the module starts, so a figure on the page is never
+  # quietly stale. The sync rewrites them every day.
+  pricing:
+    desc: Write src/data/pricing.json - what the machines the module starts by default cost an hour, on demand, in each region with images, from the lists the AWS pricing page loads (tools/pricing).
+    cmds:
+      - go run ./tools/pricing -terraform {{.TERRAFORM}} -out src/data/pricing.json
 
   sync:pr:
     desc: Commit what sources:bump and reference changed to branch sync/sources as the sync App (SYNC_TOKEN, BOT its login), and open its one pull request or update it. sync.yml runs it.
@@ -56,6 +65,7 @@ tasks:
     cmds:
       - task: sources
       - go run ./tools/refgen -spin {{.SPIN}} -terraform {{.TERRAFORM}} -brand {{.BRAND}} -shots {{.SHOTS}} -check
+      - go run ./tools/pricing -terraform {{.TERRAFORM}} -check
 
   reference:public:
     desc: Fail if what the site has of spin-terraform-aws and brand is not what they say at the commits versions.yaml pins. Needs no spin checkout, nor any credential.
@@ -64,6 +74,7 @@ tasks:
     cmds:
       - go run ./tools/sources spin-terraform-aws brand
       - go run ./tools/refgen -only terraform,brand -terraform .sources/spin-terraform-aws -brand .sources/brand -check
+      - go run ./tools/pricing -terraform .sources/spin-terraform-aws -check
 
   build:
     desc: Build the site into dist/, with llms.txt, llms-full.txt and a .md twin of every page.

src/components/Scenarios.astro

@@ -0,0 +1,43 @@
+---
+// The cost page's three scenarios (src/lib/pricing.ts), a column a region. Its Markdown twin is
+// the same table (scenariosMarkdown, src/lib/pages.ts).
+import { dollars, regions, scenarios } from '../lib/pricing';
+
+const rows = scenarios();
+---
+
+<table class="scenarios">
+	<thead>
+		<tr>
+			<th>Scenario</th>
+			<th>What runs</th>
+			{regions.map((r) => <th class="num">{r}<br /><span class="unit">$ a month</span></th>)}
+		</tr>
+	</thead>
+	<tbody>
+		{
+			rows.map((s) => (
+				<tr>
+					<td><strong>{s.name}</strong></td>
+					<td>{s.what}</td>
+					{regions.map((r) => <td class="num">{dollars(s.monthly[r])}</td>)}
+				</tr>
+			))
+		}
+	</tbody>
+</table>
+
+<style>
+	.num {
+		text-align: right;
+		font-family: var(--sl-font-mono);
+		font-variant-numeric: tabular-nums;
+		white-space: nowrap;
+	}
+	.unit {
+		font-family: var(--sl-font);
+		font-weight: normal;
+		font-size: var(--sl-text-xs);
+		color: var(--sl-color-gray-3);
+	}
+</style>

src/content/docs/aws/cost.mdx

@@ -3,12 +3,28 @@ title: Cost
 description: "What an installation costs on AWS: the small part that runs all the time, the runners that run only while workspaces do, and the settings that change it."
 ---
 
+import Scenarios from '../../../components/Scenarios.astro';
 import Value from '../../../components/Value.astro';
+import { generated, published } from '../../../lib/pricing';
 
 An installation has two kinds of cost: a small one that runs all the time, and runners, which
 run only while workspaces do. Prices depend on your region and change; use the
 [AWS Pricing Calculator](https://calculator.aws/) with the sizes below.
 
+## Three months, priced
+
+The module's default machines, on demand, in the regions Spin OS has images in, at the prices
+the AWS pricing page listed on {published} (the record was written on {generated}, and the
+daily sync rewrites it):
+
+<Scenarios />
+
+Runners are spot by default, and a spot runner costs a fraction of the on-demand hour shown:
+the calculator has your region's spot price, and `aws ec2 describe-spot-price-history` today's.
+Not in the table: what the volumes bucket holds, at S3 Standard's price per GB a month, and
+what leaves the region, at EC2's price per GB - both depend on what your workspaces do, and the
+calculator has both.
+
 ## All the time
 
 | Resource | Default size |

src/data/pricing.json

@@ -0,0 +1,93 @@
+{
+	"generated": "2026-10-26",
+	"published": "2026-10-23T22:13:55Z",
+	"source": "https://b0.p.awsstatic.com/pricing/2.0/meteredUnitMaps/ec2/USD/current/ec2-ondemand-without-sec-sel/\u003cregion\u003e/Linux/index.json",
+	"machines": {
+		"controlPlane": "t8i.medium",
+		"proxy": "t8i.micro",
+		"runners": [
+			"m8id.8xlarge",
+			"c8id.8xlarge",
+			"r8id.8xlarge",
+			"m8id.12xlarge",
+			"c8id.12xlarge"
+		],
+		"maxRunners": 1
+	},
+	"regions": {
+		"us-east-1": {
+			"c8id.12xlarge": {
+				"hourly": 2.66112,
+				"vcpu": 48,
+				"memory": "96 GiB"
+			},
+			"c8id.8xlarge": {
+				"hourly": 1.77408,
+				"vcpu": 32,
+				"memory": "64 GiB"
+			},
+			"m8id.12xlarge": {
+				"hourly": 3.13248,
+				"vcpu": 48,
+				"memory": "192 GiB"
+			},
+			"m8id.8xlarge": {
+				"hourly": 2.08832,
+				"vcpu": 32,
+				"memory": "128 GiB"
+			},
+			"r8id.8xlarge": {
+				"hourly": 2.66112,
+				"vcpu": 32,
+				"memory": "256 GiB"
+			},
+			"t8i.medium": {
+				"hourly": 0.04992,
+				"vcpu": 2,
+				"memory": "4.0 GiB"
+			},
+			"t8i.micro": {
+				"hourly": 0.01248,
+				"vcpu": 2,
+				"memory": "1.0 GiB"
+			}
+		},
+		"us-west-2": {
+			"c8id.12xlarge": {
+				"hourly": 2.66112,
+				"vcpu": 48,
+				"memory": "96 GiB"
+			},
+			"c8id.8xlarge": {
+				"hourly": 1.77408,
+				"vcpu": 32,
+				"memory": "64 GiB"
+			},
+			"m8id.12xlarge": {
+				"hourly": 3.13248,
+				"vcpu": 48,
+				"memory": "192 GiB"
+			},
+			"m8id.8xlarge": {
+				"hourly": 2.08832,
+				"vcpu": 32,
+				"memory": "128 GiB"
+			},
+			"r8id.8xlarge": {
+				"hourly": 2.66112,
+				"vcpu": 32,
+				"memory": "256 GiB"
+			},
+			"t8i.medium": {
+				"hourly": 0.04992,
+				"vcpu": 2,
+				"memory": "4.0 GiB"
+			},
+			"t8i.micro": {
+				"hourly": 0.01248,
+				"vcpu": 2,
+				"memory": "1.0 GiB"
+			}
+		}
+	}
+}

src/lib/pages.ts

@@ -5,6 +5,7 @@ import { featureHref } from './feature-links.mjs';
 import { nav } from './nav.mjs';
 import figures from '../data/figures.json';
 import { output } from './output';
+import { generated, published, scenariosMarkdown } from './pricing';
 import { statusLine } from './reference';
 import { storyMarkdown } from './story';
 import { twinPath } from './twin';
@@ -106,6 +107,9 @@ export function toMarkdown(d: Doc, base: string): string {
 	});
 	// A figure the code decides is its text.
 	body = body.replace(/<Value\s+name="(\w+)"\s*\/>/g, (_, name: string) => value(name));
+	// The cost page's scenarios are the same table, and the dates it names are the record's.
+	body = body.replace(/<Scenarios\s*\/>/g, () => scenariosMarkdown());
+	body = body.replace(/\{published\}/g, published).replace(/\{generated\}/g, generated);
 	// A screenshot is its alt text: a twin has no picture to show.
 	body = body.replace(/!\[([^\]]*)\]\([^)]*\.png\)/g, '*Screenshot: $1.*');
 	// What a command prints is the same block of output.

src/lib/pricing.ts

@@ -0,0 +1,74 @@
+// The cost page's scenarios, from src/data/pricing.json (tools/pricing): the machines the module
+// starts by default, priced on demand in each region Spin OS has images in, as the lists the AWS
+// pricing page loads had them on the record's date. Three months, each the one before plus
+// something: nothing running, one runner on working hours, the most runners around the clock.
+// Scenarios.astro draws them; the page's Markdown twin is scenariosMarkdown.
+import pricing from '../data/pricing.json';
+
+/** A month as AWS bills it. */
+const hours = 730;
+/** Working hours in a month: eight a day, twenty-two days. */
+const workingHours = 8 * 22;
+// What the installation's smaller parts are billed at, from AWS's pricing pages as of the
+// record's date: the public IPv4 address the proxy's elastic IP holds (an hour), and a Route 53
+// hosted zone (a month, and the installation has two).
+const ipv4Hourly = 0.005;
+const zoneMonthly = 0.5;
+const zones = 2;
+
+export interface Scenario {
+	name: string;
+	what: string;
+	/** Dollars a month, by region code. */
+	monthly: Record<string, number>;
+}
+
+export const regions = Object.keys(pricing.regions).sort();
+export const generated = pricing.generated;
+export const published = pricing.published.slice(0, 10);
+export const machines = pricing.machines;
+
+function price(region: string, type: string): number {
+	const p = (pricing.regions as Record<string, Record<string, { hourly: number }>>)[region]?.[type];
+	if (!p) throw new Error(`pricing.json: no price for ${type} in ${region}`);
+	return p.hourly;
+}
+
+/** The three scenarios, each a month in dollars per region. */
+export function scenarios(): Scenario[] {
+	const { controlPlane, proxy, runners, maxRunners } = machines;
+	const runner = runners[0];
+	const perRegion = (f: (region: string) => number) => Object.fromEntries(regions.map((r) => [r, f(r)]));
+	const idle = (r: string) => (price(r, controlPlane) + price(r, proxy) + ipv4Hourly) * hours + zones * zoneMonthly;
+	const n = maxRunners;
+	return [
+		{
+			name: 'Nothing running',
+			what: `The control plane (${controlPlane}) and the proxy (${proxy}) all month, the proxy's public IPv4 address, and two Route 53 zones. No runner is up.`,
+			monthly: perRegion(idle),
+		},
+		{
+			name: 'One runner, working hours',
+			what: `The above, and one ${runner} up ${workingHours} hours: eight a day, twenty-two days, on demand.`,
+			monthly: perRegion((r) => idle(r) + price(r, runner) * workingHours),
+		},
+		{
+			name: n === 1 ? 'One runner around the clock' : `${n} runners around the clock`,
+			what: `The above with ${n === 1 ? 'the runner' : `${n} runners (max_runners' default)`} up all month, on demand: the most the default installation can spend on runners.`,
+			monthly: perRegion((r) => idle(r) + n * price(r, runner) * hours),
+		},
+	];
+}
+
+/** A dollar figure as the table shows it. */
+export function dollars(n: number): string {
+	return `$${n.toLocaleString('en-US', { minimumFractionDigits: 0, maximumFractionDigits: 0 })}`;
+}
+
+/** The scenarios as a Markdown table, for the page's twin. */
+export function scenariosMarkdown(): string {
+	const head = `| Scenario | What runs | ${regions.map((r) => `${r} ($/month)`).join(' | ')} |`;
+	const rule = `|---|---|${regions.map(() => '---').join('|')}|`;
+	const rows = scenarios().map((s) => `| **${s.name}** | ${s.what} | ${regions.map((r) => dollars(s.monthly[r])).join(' | ')} |`);
+	return [head, rule, ...rows].join('\n');
+}