You can easily use pg_dump to do a "vanilla" backup to s3. Its a managed db service but if you wanted to run your own you can extract your data and move to a new db. The lock is not "complete" you are acting like you can't even extract your data.
"Only export your data with pg_dump" is one of those misfeatures that makes RDS mediocre. They don't really expose much of the power of the underlying DB.
you cannot ssh to RDS machine. so u need to get another EC2 machine and pg_dump over the network. the connection breaks - yes has happened to us multiple times.
RDS makes it very inconvenient to do anything other than use their managed services.
because RDS backup data storage is VERY EXPENSIVE even compared to s3. this is very deliberate.