BuddySWT: Chartering in Central America costs about the same as chartering anywhere else, but the travel there and back is a lot easier from mid America. With a captain, a bareboat plus captain from TMM in Belize can be a lot of fun. With a captain you would be free to visit the offshore atolls, including the blue hole, and some really spectacular stuff around Halfmoon Cay. May is probably too late for the whale sharks, but if they are still congregating, seeing them would be an experience of a lifetime. sailtmm.com is the web site.
There is another charter outfit in Belize. In reading comments about maintenance issues other charterers have posted, I would have concerns about using them.
There are two crewed charter boats based in Cucumber marina just south of Belize City. One cat is fun by a Mother and Father, the other is run by their son. I have seen both cats, and visited extensively with the son. We were favorably impressed. Unfortunately can't give you names.
Decades ago we used Ed Hamilton to arrange a charter. Very knowlegable, and help out in some unexpected ways.
There are many shore based trips well worth taking in Belize. There is NO night life in Belize.