I am having a private catamaran cruise the afternoon after the ceremony. Here is the company's website that I will be using. Just send them an email and they will give you a quote. I found the excursion I was interested in said something like snorkle cruise and duns river falls. Just clicked on more info and the prices came up and there was a section to click for private tours along with the prices. Hope that makes sense. I also requested just the cruise and snorkle not stopping at Dunn's Rivers Falls.
my quote is pretty high because at the time I contacted them there was only about 16 of us. so the quote was 66.00 per person, then I requested food to be served as well so thats an additional 10.00 per person. I will be contacting them early January for an updated quote and be booking them at that time. (wedding is in July 2011)
Hope that is of some help to you