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Part 6 of 7 · Payout reconciler series ~5 min read

What the payout reconciler costs

The model reads the lines no rule can type and the occasional PDF statement. The tens of thousands of report lines around them are parsed, and parsing is close to free at this size. The worked retailer sent 142 lines to the model in its first year, about twelve a month; ninety a month is a business with more providers and a marketplace fond of free text. Here is where each cent goes.

Key takeaways

  • About $2 a month at 90 lines. Roughly $4 at 300 lines.
  • One Bedrock read per unmapped line is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • The bill follows unexplained lines, not sales. A record month of trading adds rows to parse and almost nothing to the model line.
  • 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 payout reconciler at three volumesA stacked bar chart with three bars, one per volume tier: 25 lines totalling about $2, 90 lines totalling about $2, and 300 lines totalling about $4. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per unmapped line, 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~$1.5225 lines~$2.290 lines~$4.39300 linesBedrock — one read per unmapped lineSES — 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 unmapped line — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 90 linesHow it scales
Bedrock read$0.45Linear. One call per unmapped line, roughly 1,800 in and 200 out tokens.
SES$0.05Linear. About 1 messages per unmapped line.
DynamoDB + S3$0.66Storage 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 call per unmapped line, against a small model, plus one per PDF statement, which is a handful a month and is inside the volumes above. Choosing one of eleven types for a sentence of free text is classification, not reasoning, and a larger model is paying for reasoning the task never uses.

The three ways this bill surprises you

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

  • Sending settlement reports through the model. They are fixed-header exports with a type code on nearly every row. Parse them; a model over a year of reports costs more than the reconciliation saves and is less reliable than a column lookup.
  • Forgetting confirmed answers. Without the remembered-wording step, the same Terminal rental line is read every month for ever. The lookup is what makes the model line shrink instead of grow.
  • Re-pulling every report since the start of trading. Provider reporting windows roll and their APIs are rate-limited. Fetch what is new since the last cursor and append; the stored lines are the record, not the provider’s export.

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. 25 lines, about $2. 90 lines, about $2. 300 lines, 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~$125 lines~$290 lines~$2300 lines~$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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