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Part 6 of 7 · Supplier lead time watcher series ~5 min read

What the supplier lead time watcher costs

There is no model in this system and almost nothing is sent: a drift alert fires for a supplier a few times a year, not per order. Three hundred purchase orders a month is a busy small manufacturer. Here is where each cent goes.

Key takeaways

  • About $2 a month at 300 orders. Roughly $3 at 1,200 orders.
  • One Bedrock read per purchase order is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • Alerts are rare by design, so messaging barely registers at any volume.
  • 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 supplier lead time watcher at three volumesA stacked bar chart with three bars, one per volume tier: 80 orders totalling about $1, 300 orders totalling about $2, and 1,200 orders totalling about $3. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per purchase order, 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~$1.3680 orders~$1.69300 orders~$3.061,200 ordersBedrock — one read per purchase orderSES — 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 purchase order — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 300 ordersHow it scales
Bedrock read$0.00Linear. One call per purchase order, roughly 1,800 in and 200 out tokens.
SES$0.15Linear. About 0.08 messages per purchase order.
DynamoDB + S3$0.33Storage 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 a handful of drift alerts a month across the whole supplier base.

The three ways this bill surprises you

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

  • Recomputing every distribution nightly. A distribution changes when an order is received. Compute on receipt, not on a schedule.
  • Alerting on single late orders. Not a cost problem but the reason a system like this gets muted, after which it costs the same and does nothing.
  • Copying the purchase order table. This reads records that already exist. A second copy is cost plus a synchronisation 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. 80 orders, about $1. 300 orders, about $2. 1,200 orders, 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~$180 orders~$1300 orders~$21,200 orders~$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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