krehfish, I agree and also with Otter. On that budget, a visit to Caye Caulker would be nice and cheap. Seperately, snorkeling to Hol Chan and Shark Ray Alley. Expect to pay between $40 - $50 per person for the snorkeling, rentals, park fee and tip. Get in touch with Clifford and Eric. They're top notch!

Otherwise, on $300 for the whole week, lots of cheap eats and walking or bike riding around will be good.