Make a friend. Talk to people in the customs line. Share a ride. There are some interesting people traveling about. It never hurts to call out if anyone is going downtown. The cab fee hurts a little but you'll live.
the boats at water taxi also go to San Pedro so check and see if anybody is going to caye caulker or san pedro via water taxi..might help even more for a wider frame to work with I believe it's $35 BZ to the city .... Maralyn