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Part 6 of 7 · Utility meter reader series ~5 min read

What the utility meter reader costs

There is no model in this system and the data is small: a half-hourly meter produces about seventeen hundred readings a month. Fifteen meters is several sites or one site with sub-metering. Here is where each cent goes.

Key takeaways

  • About $1 a month at 15 meters. Roughly $1 at 60 meters.
  • One Bedrock read per meter is the only line that scales. Everything else is rounding.
  • Nothing is always-on, so a quiet month genuinely costs almost nothing.
  • The whole bill is effectively fixed; half-hourly data across sixty meters is still a trivial 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 utility meter reader at three volumesA stacked bar chart with three bars, one per volume tier: 4 meters totalling about $1, 15 meters totalling about $1, and 60 meters totalling about $1. Each bar is stacked from bands. The largest and fastest-growing is Bedrock, one read per meter, 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$0.5$1$1.5$2~$1.244 meters~$1.2615 meters~$1.3460 metersBedrock — one read per meterSES — 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 meter — is the only part that grows; the orange fixed band is the same 86 cents at every volume.

Line by line

LineAt 15 metersHow it scales
Bedrock read$0.00Linear. One call per meter, roughly 1,800 in and 200 out tokens.
SES$0.01Linear. About 0.9 messages per meter.
DynamoDB + S3$0.28Storage 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. Messaging is a monthly findings summary per meter group, not per reading.

The three ways this bill surprises you

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

  • Storing one item per half-hourly reading. Batch a day per meter into one item and the write count falls by nearly fifty times.
  • Fetching weather data per reading. Degree days are one value per day per location. Fetch once daily and cache.
  • Building a live dashboard. Not a cost problem so much as a waste: nobody opens it, and the findings are what matter.

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. 4 meters, about $1. 15 meters, about $1. 60 meters, about $1. 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~$14 meters~$115 meters~$160 meters~$1One 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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