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Part 6 of 7 · Utility bill watcher series ~5 min read

What the utility bill watcher costs

A single-site business gets about two dozen utility bills a year; a dozen sites across four utilities gets a couple of hundred. Either way this is the cheapest system in the series to run, because the volume is tiny and nothing is always-on. Here is where each cent goes.

Key takeaways

  • About $2 a month at 60 bills. Roughly $4 at 200 bills.
  • One Bedrock read per bill is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • Volume is genuinely tiny — a dozen sites is a couple of hundred bills a year, not a month.
  • 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 utility bill watcher at three volumesA stacked bar chart with three bars, one per volume tier: 24 bills totalling about $2, 60 bills totalling about $2, and 200 bills totalling about $4. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per bill, 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~$1.524 bills~$1.9260 bills~$3.51200 billsBedrock — one read per billSES — asks, results, receiptsTextract — every bill pageS3 + 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 bill — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 60 billsHow it scales
Bedrock read$0.28Linear. One call per bill, roughly 1,800 in and 200 out tokens.
Textract$0.31Linear at $0.0052 per bill.
SES$0.03Linear. About 0.6 messages per bill.
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.

Textract is the largest per-bill line because utility bills run to several pages and the layout has to be extracted from all of them. It is still fractions of a cent, and the volume is a couple of hundred a year rather than a couple of hundred a month.

The three ways this bill surprises you

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

  • Re-reading resent bills. Suppliers resend constantly — reminders with the original attached, corrected copies, statements containing last month’s bill as a page. Without the duplicate test in front of Textract you pay to extract the same bill five times.
  • A retry loop on an unparseable PDF. Some supplier PDFs are a single scanned image at low resolution, and Textract will return very little. A dead-letter queue with a maximum receive count of three turns that into one flagged bill instead of an infinite loop.
  • Log retention left at never. With volume this low the logs will comfortably out-cost the compute within a year. Thirty days of retention is the highest-return setting here by a wide margin.

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. 24 bills, about $2. 60 bills, about $2. 200 bills, 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~$124 bills~$260 bills~$2200 bills~$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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