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Part 6 of 7 · Credit limit reviewer series ~5 min read

What the credit limit reviewer costs

The model runs once per credit application, not per order: the headroom check is a single key lookup and costs nothing. Eighty reviews a month is a business onboarding steadily and watching its ledger properly. Here is where each cent goes.

Key takeaways

  • About $2 a month at 80 reviews. Roughly $3 at 320 reviews.
  • One Bedrock read per review is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • The headroom check is a point read, so the order-taking path costs the same whether you check ten orders a day or a thousand.
  • 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 credit limit reviewer at three volumesA stacked bar chart with three bars, one per volume tier: 20 reviews totalling about $1, 80 reviews totalling about $2, and 320 reviews totalling about $3. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per review, 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$1$2$3$4~$1.3320 reviews~$1.6280 reviews~$2.76320 reviewsBedrock — one read per reviewSES — 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 review — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 80 reviewsHow it scales
Bedrock read$0.25Linear. One call per review, roughly 1,800 in and 200 out tokens.
SES$0.05Linear. About 1.6 messages per review.
DynamoDB + S3$0.29Storage 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 credit application against a small model, extracting fields from a PDF the customer sent. Orders do not trigger a read at all — the check at the point of order is a single-item lookup, which is why the volume that scales is reviews rather than sales.

The three ways this bill surprises you

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

  • Recomputing exposure by summing the ledger on every check. Store the number and move it on events; a full scan per order keyed is how a two-dollar system becomes a hundred-dollar one.
  • Re-reading filed accounts on a schedule. They change once a year. Read them when the filing date moves, not every month.
  • Alerting on every overdue invoice. That is invoice chasing, it belongs elsewhere, and routing it through here doubles the messaging for no decision.

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. 20 reviews, about $1. 80 reviews, about $2. 320 reviews, about $3. 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~$120 reviews~$180 reviews~$2320 reviews~$3One 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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