Have you thought about Grand Turk in the Turks and Caicos? I live and work here and can attest to the fact that it is very quiet and relaxing. The diving always gets rave reviews and is consistently rated as one of the best in the Caribbean, if not the world. Lots of types of fish, and quite a few turtles, stingrays, and sharks here. One group even saw a hammerhead last week. There's some beautiful diving here, swim-throughs, the 7000' wall, lots of corals, etc. It's very quiet here - which makes for a nice, relaxing get-away. There's only one main road right along the beach that houses the few small hotels/guest houses and dive shops. From what I hear, we're less expensive than Provo since we don't really do the mega-resort thing here. You can easily walk from most accommodations to most of the dive shops.
I'm happy to answer any other questions you may have, please feel free to PM me.
I'm happy to answer any other questions you may have, please feel free to PM me.