> The db.r3.8xlarge on RDS Postgres all in with 3000 provisioned IOPS (just provisioning for writes, all reads should be served from memory) and 1.5TB storage ends up around $6k. A 3 year reservation will get that down to $3k. > Comparable DynamoDB (3000 write units, 3000 read units, reserved IOPS) comes out to $1500.

Note those aren't really comparable numbers - postgres will often collapse writes from concurrent sessions / statements.