This might help.

http://www.negrilcruises.com/index.html

I took the Tortuga trip recently and it was alright, nothing to write home about, but alright. Just need to show up at Margaritaville before 2PM with $60.00 in hand and you are on the boat but check first because thing might have changed. $60 got you a bag of chips and all you can drink draft beer, rum punch, and hard liquor. I just like to out on the water so I enjoyed it.