On budgetting, why don't you take advice from people who already live here? There are always extras and although they're often difficult to analyse and quantify, that doesn't stop them happening. Accept the sorts of amounts that people have been saying it will cost you to live here. If your finances are so tight that careful analysis of detail could sway your decision then you're sailing too close to the wind. Belize is an expensive place to live, AC especially.
A point of detail. When I suggested buying a bike rather than renting one I thought you were staying for a month or more. For a short stay certainly rent. But I meant what I said about locks - most of those available here are rubbish.