When I was in CC in Feb 2006, I talked to the guy who runs Anglers Abroad. I only saw him because his shop was beside the place I stayed at (Maria's Place, right beside the split).
I was doing DIY and it was my first attempts at bones. He seemed like a nice guy and gave me some tips and I bought a couple flies from him but I can't really comment on his guiding skills or prices. I see on his website that he offers overnight trips to a remote offshore island as well.
I did manage to hook a half dozen bones and landed 2 (as well as some barracuda and snapper) just walking around the island.
I noticed on a map of the Caye listings for three others: Eloy's Fishing, Gabriel's Fishing and Northern Fisherman Cooperative
I am pretty jealous you are heading down there. Best of luck.