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Part 6 of 7 · Age check logger series ~5 min read

What the age check logger costs

The model reads photographs of handwritten pages, and that is the whole of the variable bill. Till exports are parsed, rates are arithmetic, and a pack is a handful of queries. Three hundred and sixty pages a month is four stores photographing the book at the end of three shifts a day. Here is where each cent goes.

Key takeaways

  • About $6 a month at 360 pages. Roughly $16 at 1,080 pages.
  • One Bedrock read per register page is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • The bill tracks shifts, not sales. A busier Saturday does not photograph any more pages.
  • The duplicate test runs before the read, so resends are free.
  • The three real risks: a retry loop, storage nobody expires, and a bigger model than the job needs.

The bill at three volumes

These are US East prices at the time of writing, at three volumes that bracket most small businesses. Find the bar closest to your own and read across.

Monthly cost of the age check logger at three volumesA stacked bar chart with three bars, one per volume tier: 90 pages totalling about $3, 360 pages totalling about $6, and 1,080 pages totalling about $16. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per register page, in teal. Then SES for the messages, in pink. Then S3 and DynamoDB storage in green. Then a fixed orange band for Secrets Manager and AWS Budgets, which is eighty-six cents at every volume. Then a grey band for Lambda, SQS and CloudWatch. A note says the read is the only bar that grows with the business and the orange band never moves.$0$5$10$15$20~$2.5390 pages~$6.19360 pages~$15.981,080 pagesBedrock — one read per register pageSES — asks, results, receiptsS3 + DynamoDBFixed — Secrets Manager, BudgetsLambda, SQS, CloudWatchThe read is the only bar that grows with the business. The orange fixed band never moves.
Fig 1. The monthly bill at three volumes. The teal band — one model read per register page — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 360 pagesHow it scales
Bedrock read$3.96Linear. One call per register page, roughly 1,800 in and 200 out tokens.
SES$0.19Linear. About 0.4 messages per register page.
DynamoDB + S3$0.77Storage grows with what you retain, not with throughput.
Lambda + SQS$0.12Linear, and effectively free at this scale.
CloudWatch$0.16Flat, if you set retention. Unbounded if you do not.
Secrets Manager$0.40Flat. One secret, $0.40 a month.
AWS Budgets$0.46Flat. Two actions, so you find out before the bill does.

Roughly one model read per page photograph, against a vision-capable mid-tier model. A refusals book page is a dozen short handwritten lines in fixed columns, and the difficulty is the handwriting rather than any reasoning. A frontier model reads the same dozen lines for several times the price and still cannot read a signature, which is why signatures are resolved from the rota.

The three ways this bill surprises you

Every one of these has happened to somebody, and all three are cheap to prevent.

  • Re-reading closed pages. A page photographed at the end of three shifts is three reads of a page that has mostly not changed, and that is fine, because the retake request depends on it. Going back over the whole book when a rule or a join changes is not; the transcription is already stored.
  • Running a model over the till export. It is fixed-format rows with a header. Reading it with a model would cost more than everything else in the system combined and add nothing except the chance of a misread time.
  • Keeping every photograph at full resolution forever. The transcription and the joins are the working record. The photographs are evidence of what the book said, and they need a retention rule the business has actually decided, not the default of never.

What it costs when nothing happens

This matters more than the headline number for a seasonal business. In a month with nothing to process the bill is the fixed band: Secrets Manager at forty cents, AWS Budgets at forty-six, and a few cents of storage. Call it a dollar. There is no instance to stop and nothing to remember to turn off.

The monthly bill at four volumes plus one failure modeA horizontal row of five boxes. Quiet month, about one dollar. 90 pages, about $3. 360 pages, about $6. 1,080 pages, about $16. And one bad retry loop, about two hundred dollars. A note says four of these are the design working and the fifth is a missing dead-letter queue.THE BILL, AT A GLANCEQuiet month~$190 pages~$3360 pages~$61,080 pages~$16One bad loop~$200Four of these are the design working. The fifth is a missing dead-letter queue.
Fig 2. The bill at a glance, including the one that is not a volume at all. A retry loop with no dead-letter queue costs more than every legitimate use of the system put together.
  • Management
  • Analytics
  • Front-end & mobile

Set these on day one

  • A dead-letter queue on every SQS queue, with a maximum receive count of three.
  • Thirty-day retention on every CloudWatch log group. There is no default that is safe.
  • An S3 lifecycle rule on the object prefix, tiering at 90 days and expiring at your actual record-keeping horizon.
  • Two AWS Budgets actions — one that emails at half your expected spend, one at double it. The second is how you find out about a loop in an hour instead of a month.
  • Provisioned concurrency: none. Nothing here is latency-sensitive enough to justify paying for a warm function.

Next: the same system drawn for engineers — service names, resource identifiers, IAM scopes, table schemas and the model id.

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