What it costs to run a SaaS on Lambda and one DynamoDB table
I run a small SaaS on AWS with no servers: a few Lambda functions, one DynamoDB table and a CDN. People often say this kind of setup costs "about nothing" until it suddenly doesn't, so here's the real bill for October, the month it launched, broken down by service, plus what I think changes as it grows. The numbers come from AWS Cost Explorer, filtered to a tag that every resource for this…
Running a small Software as a Service (SaaS) on AWS using only Lambda functions, one DynamoDB table, and a CDN generates a minimal monthly bill. The October bill for the setup was $0.74, with fixed costs accounting for 88% of the total. The most significant fixed costs were the Route 53 DNS zone ($0.50) and the KMS encryption key ($0.15), making up 88% of the bill.
Traffic-dependent costs, such as Lambda usage, CloudFront requests, and DynamoDB operations, contributed almost nothing to the total. The most variable cost was S3, which totaled $0.08 due to requests and writes. The Cognito login service and AI summaries were also negligible in this specific case. Fixed costs like the domain registration and API Gateway throttling are minimal in comparison.
The setup highlights the importance of avoiding VPCs and secondary indexes and using arm64 Lambdas to keep costs low.
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