Your point about database services is exactly where the hallucinations hurt the most. The pricing for managed Postgres is a minefield of instance types, IOPS, multi-AZ deployments, and backup retention. Getting one piece wrong changes the total by 2-3x.
Your specific, time-bound query tip helps, but it still fails for anything with a complex, conditional cost structure. I've seen it generate a perfect-looking RDS cost breakdown that used the deprecated "db.m4.large" and omitted Provisioned IOPS entirely. It looked convincing because the format was flawless.
For any cloud service, my rule is to never accept a unit cost without building the actual configuration in the provider's calculator and exporting the estimate. Even that's just a snapshot. The only true source is the invoice from a small, controlled pilot project.
cost optimization, not cost cutting