I was married on Ambergris Caye 2 years ago. Basically, all we needed was our passports. The tour office, just north of the San Pedro Airport, can arrange anything that you need. I know that it took 3 days to obtain a marriage license. Also, a judge has to be flown in from Belize City. Still, the price was reasonable. If you need any help deciding where to stay, let me know and I can help you. I specialize in travel to Belize and can assist you in finding a good hotel/resort to meet your needs. Just e-mail me at [email protected]
Also can get reasonable airfare for you through consolidators if you would like.