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Part 6 of 7 · Lost property matcher series ~5 min read

What the lost property matcher costs

The model runs once per claim, not per item: logging is a form with a picklist and a photograph. Two hundred and forty claims a month is a busy venue. Here is where each cent goes.

Key takeaways

  • About $2 a month at 240 claims. Roughly $4 at 900 claims.
  • One Bedrock read per claim is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • Photographs are the only storage that grows, and resizing on upload keeps even a busy year under a dollar.
  • 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 lost property matcher at three volumesA stacked bar chart with three bars, one per volume tier: 60 claims totalling about $1, 240 claims totalling about $2, and 900 claims totalling about $4. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per claim, 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$2$4$6$8~$1.4960 claims~$2.09240 claims~$4.28900 claimsBedrock — one read per claimSES — 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 claim — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 240 claimsHow it scales
Bedrock read$0.34Linear. One call per claim, roughly 1,800 in and 200 out tokens.
SES$0.20Linear. About 3.4 messages per claim.
DynamoDB + S3$0.39Storage 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.

The read is one call per claim against a small model, turning whatever somebody wrote or dictated into the same four fields. Logging an item never calls a model: it is three taps and a photograph, and the ninety-second budget is the reason the system works at all.

The three ways this bill surprises you

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

  • Storing photographs at full phone resolution. Resize on upload. A staff member confirming a match needs to recognise a jacket, not read a care label.
  • Running image recognition on every item. It is not what makes the match work, and it turns a two-dollar system into a forty-dollar one for a ranking that zone and date already produce.
  • Re-running open claims against the whole inventory nightly. Check new items against open claims, which is a handful of comparisons, not the cross product.

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. 60 claims, about $1. 240 claims, about $2. 900 claims, about $4. 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~$160 claims~$1240 claims~$2900 claims~$4One 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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