Free to play. I created a group for us Sharks to join up and compete against each other. Group name is Sharks. Group # 1772. Password is Sharks1. This link is to the how to play page and if you're interested you can take it from there.
I remember a bunch of us did this last year and a thread was created here in the Main Tank for it. I have a thread in Tank Games, but I don't think that forum gets to many hits.