Is AWS RDS billing purely based on RAM/IO and storage? or is there any additional per database charges?

For my RDS deploy, If I have 1 PostgreSQL DB that has all my data but only receives 2000 queries per day vs if I have 4 PostgreSQL DBs that have the same relations as the 1 DB but those relations are split up on the 4 DBs and the 4 DBs will collectively receive the same 2000 queries per day... will the bill between the two different setups be essentially the same amount? The assumption being that the "size" of the data in 1DB vs 4DBs is exactly the same.

I want to split the data across multiple databases to make reporting for different modules in my system easier.