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Part 6 of 7 · Abandoned form recoverer series ~5 min read

What the abandoned form recoverer costs

There is no model in this system and the message volume is low by design, because two thirds of abandonments produce nothing. Four hundred abandonments a month is a reasonably busy enquiry form. Here is where each cent goes.

Key takeaways

  • About $2 a month at 400 abandonments. Roughly $4 at 1,500 abandonments.
  • One Bedrock read per abandonment is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • Only about a third of abandonments result in a message, which keeps the messaging line small.
  • 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 abandoned form recoverer at three volumesA stacked bar chart with three bars, one per volume tier: 100 abandonments totalling about $1, 400 abandonments totalling about $2, and 1,500 abandonments totalling about $4. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per abandonment, 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~$1.39100 abandonments~$1.85400 abandonments~$3.561,500 abandonmentsBedrock — one read per abandonmentSES — 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 abandonment — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 400 abandonmentsHow it scales
Bedrock read$0.00Linear. One call per abandonment, roughly 1,800 in and 200 out tokens.
SES$0.21Linear. About 0.35 messages per abandonment.
DynamoDB + S3$0.34Storage 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.

There is no read line: nothing here calls a model. The messaging band assumes roughly a third of abandonments pass the basis check, which matches what the gates in Part 3 actually do.

The three ways this bill surprises you

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

  • Capturing on every keystroke. Not primarily a cost problem, though it is one at volume: a write per keystroke across a busy form is a lot of writes for data you delete in seven days.
  • Never expiring partial data. A table of half-finished forms accumulating for years is a storage cost and a much larger data question. Seven days is generous.
  • Log retention left at never. These logs contain partial form contents, which makes unbounded retention both a cost and a problem.

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. 100 abandonments, about $1. 400 abandonments, about $2. 1,500 abandonments, 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~$1100 abandonments~$1400 abandonments~$21,500 abandonments~$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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