Comment by miyuru

You can calculate how much RDS is gonna cost you per month beforehand.

In fact, it is slightly cheaper at AWS.

Ondemand PostgreSQL, Single Node, 1vCPU, 1GB MEM, 10GB Storage is $15 at DO

Ondemand PostgreSQL, Single Node, 2vCPU, 1GB MEM, 10GB Storage is $14.29 at AWS (db.t3.micro at us-east-2)

if reserved for 1yr no upfront

Reserved PostgreSQL, Single Node, 2vCPU, 1GB MEM, 10GB Storage is $10.57 at AWS (db.t3.micro at us-east-2)

Or you can use ARM and go lower.

Ondemand PostgreSQL, Single Node, 2vCPU, 1GB MEM, 10GB Storage is $12.83 at AWS (db.t4g.micro at us-east-2)