let the tour desk know the first day you get there that you want to go and maybe they can team you up with others. the more that go, the cheaper it is. if you go- post on the MB how the fishing was please! we will be going in 3 weeks!
The tour desk sets it up. There are a few companies both in Ocho and Negril that do it. I am 99% (WEATHER PERMITTING) sure we are going so I will be sure to tell the MB all about it when I return. It generally runs about $300 a couple if there are only 2 people. It decreases significantly if you have others with you. You go out pretty far- so don't go out with a hangover. Even if you handle cruises and boats on lakes well- bring some dramamine or motion sickness pills - its a while new world way out there in a tiny boat!