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Part 6 of 7 · Email assistant series ~3 min read

What the email assistant costs

A coffee a month at typical SMB volume. The fixed cost is roughly nothing. Everything else scales with the number of emails actually handled by the brain — not the noisy ones the routing rules already filtered out.

Key takeaways

  • Fixed cost is roughly zero: Lambda, S3, DynamoDB, and CloudWatch all sit inside always-free quotas at SMB volume; quiet weeks bill basically nothing.
  • SES inbound is about $0.10 per 1,000 chunks of 256 KB — a 200-emails-a-day inbox runs roughly 60¢/month.
  • SES outbound is $0.10 per 1,000 emails sent, and only 30–50% of brain-handled mail auto-sends, so outbound stays in pennies.
  • Bedrock Haiku tokens run $1–$3/month for a 200-emails-a-day inbox after the cleanup in Part 3 cuts inputs five-to-ten-fold.
  • Most small businesses land between $2 and $5/month; a $10 AWS Budgets alarm catches anything strange, and 7-day CloudWatch retention from day one keeps log storage from drifting.
Cost structure: three tiers A horizontal flow with three labeled tiers showing where the bill actually goes. From left to right: Tier 1, Always-free — Lambda invocations, S3 storage at small volume, DynamoDB pay-per-request reads and writes, CloudWatch log retention at 7 days, the S3 vector index for the knowledge file. Tier 2, Per-email pennies — SES inbound (about $0.10 per 1000 emails), SES outbound (about $0.10 per 1000 emails), Bedrock Haiku tokens for the brain (typically a fraction of a cent per email). Tier 3, Optional — SES domain identity verification (free), MailFrom subdomain for deliverability, SES sandbox-removal request once you go live. A bottom note reads: a typical SMB inbox at 200 emails a day lands in coffee-money territory — usually under five dollars a month. tier 1 Always-free Lambda invocations ~ $0.00 S3 storage ~ $0.05 DynamoDB pay-per-request ~ $0.10 CloudWatch (7-day retention) ~ $0.10 S3 vector index tier 2 Per-email pennies SES inbound $0.10 / 1000 emails SES outbound $0.10 / 1000 emails Bedrock Haiku tokens ~ $0.001 / email S3 vector queries ~ fraction of a cent tier 3 Optional SES domain identity free MailFrom subdomain free Sandbox removal free, one form Custom domain your registrar ~ 200 emails a day → under five dollars a month, often under three.
Fig 6. Three tiers of cost. The bill scales smoothly with email volume; the floor is nearly zero.

The fixed cost is roughly nothing

Unlike the voice agent in the previous series, the email assistant has no fixed monthly floor. There’s no phone number to rent. If the inbox is quiet for a week, the bill for that week is basically zero. Lambda, S3, DynamoDB, and CloudWatch all sit in the always-free tier at the volumes the assistant uses, and the vector index for the knowledge file is small enough to round to a few cents a month.

The flat costs you do pay are the AWS account’s background ones — small storage fees, a handful of Lambda runs from the sync job, log retention. Together, well under a dollar a month at small-business volume.

The variable cost is per-email pennies

Three things scale with email volume:

  • SES inbound — about $0.10 per 1,000 incoming chunks, where one chunk is 256 KB. A short text email is one chunk; a long thread or a heavy attachment can be a few. At 200 short emails a day, that’s about 60 cents a month.
  • SES outbound — about $0.10 per 1,000 emails sent. The auto-reply rate from part 4 is roughly 30–50% of brain-handled mail, so outbound is much smaller than inbound. Pennies a month at small-business volume.
  • Bedrock Haiku tokens — roughly a fraction of a cent per email after the cleaning and search steps from posts 3 and 5 cut the input down. A 200-emails-a-day inbox usually lands at one to three dollars of Bedrock spend per month.

Add it up: most small businesses end up between $2 and $5 a month total. The assistant pays for itself the first morning you don’t spend an hour answering “what are your hours?” for the tenth time.

Three traps you’re avoiding

  • Per-seat AI email tools. Most “AI email assistant” products charge $20–$50 per inbox per month, no matter how much you use them. You’re trading a flat subscription for pay-per-use that mostly comes in pennies.
  • Sending the whole thread to the model. The reader strips quoted history before the brain sees anything. A simple setup that doesn’t do this pays the model to read every previous reply quoted back at it; you don’t.
  • Logs that quietly grow. CloudWatch keeps logs for only 7 days from day one. Without that, log storage slowly drifts up forever. Seven days is enough to debug live, and the audit table carries the long-term record.

When this stops being cheap

The math changes at high volume. A busy support inbox at 5,000 emails a day with a draft-most policy might land at $30–$60 a month — still cheaper than the per-seat products, but no longer coffee money. At that point the cost is mostly model tokens, and switching the brain to a smaller model or tightening the search pays off quickly.

For everyone below that — and that’s most small businesses — the bill is small enough that a $10 monthly AWS Budget alarm catches anything strange before you’d notice on the credit card.

In plain words

The fixed bill is nearly zero. The variable bill is cents per email. A typical small-business inbox runs at coffee-money for the whole month. Set a budget alarm that fits your expected volume and the bill can’t surprise you.

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