We've been 3 times, once twinned with Sri Lanka, and have stayed on Laguna Beach (now re-named), Maayafushi (not available to UK any longer) and Vilamendhoo (great snorkelling but much beach erosion).
Your budget is good, I would def recommend either AI or HB depending on how much you drink and whether you wish to try any other restaurants that may be on the island you choose. Most durations are 7 or 14 nights though as it's mainly charter airlines who fly direct to Male on a weekly basis although Emirates is another option via Dubai.
Best idea is to trawl the brochures for islands in your price range then check out the reviews on www.tripadvisor.com. We always do this as it's easy to get carried away with the top, very pricey resorts online otherwise!
What time of year are you looking at as high season is Dec - Apr and our summer can be quite wet and stormy although the weather has been adversely affected the last few years even in Feb/Mar.