Aloha,
So um, both servers are free... not sure why you think you have to pay.
We have the servers separated because you have a big pool of H2O between us and the EU folks, which lends to connectivity issues sometimes. That and we have separate teams to better support those players (languages and culture etc). You can create an account on both servers with the same credentials.
There is a big difference from EU to NA in terms of interaction though... The EU server tends to be a bit more, um, not-friendly, in terms of their interactions with each other.
-Hapa