Sounds awesome. Maybe the wife and I will join you there once someone gives us the answer.

I'm hoping that such a place exists and the person who knows about it won't mind sharing. But here are the obvious difficulties: You're talking about ultra-high season in Thailand, so to stay in that price range I suppose you'd need someplace remote (difficult to get to) and as yet unappreciated. At a Thai oriented hotel, not speaking Thai might be an obstacle (though I think you'd be OK if you're patient). As for crystal-clear, calm waters, the best I can remember is around the Phi Phi islands (but not many hotels there and they will be super-expensive, out of your price range). Maybe you could settle for swimmable with a clean beach. The west coast of southern Thailand is nice that time of year (way better than Bali, in my opinion, especially given your criteria).

According to travelfish (travelfish.org/feature/43), "If you're tiring of hanging out in tourist ghettos, there's an ample supply of islands where tourism is but a small part of the local economy. Ko Yao Noi is an excellent choice, as is Ko Jum, Ko Libong and Ko Kut. Ko Kut in particular attracts a lot of Thai weekenders, so as a foreigner you'll often be in the minority -- a refreshing change from most Thai islands."

Be sure to write a review after your trip.