Well, almost free.
Gadling.com posted about two resorts in St. Maarten that will pay for your wedding (i.e. the ceremony and reception), if you and 20 of your nearest and dearest are willing to book a 7-night all-inclusive stay. At $300+/night for all the all-inclusive rooms, I doubt I could persuade 2 of my friends to come with me, much less 20.
But if you're already planning to do a wedding in the Caribbean and have a budget to accommodate this, this would be a fantastic deal. Weddings at resorts can be pretty darned expensive, and this might be worth your while. (However, I would argue it's also worth your while to see how much the standard wedding costs at the resort MINUS the requirement for a 7-night all-inclusive stay.)
Anywho, to check out the deals for yourself, see: