How about Grand Cayman? There's a great five-and-a-half-mile-long beach (called "Seven Mile Beach" in a triumph of advertising over accuracy) with a bazillion places to stay on that side of the road (walk out your back door onto the sand) or the other (slightly longer walk, obviously). They cater to all budgets and tastes. And you can always head over to one of the fancier ones to hang out in the lobby and pretend you're really staying there if you want to.