I had a blast on this a few years ago. Since I had been to Nassau and seen everything there was to see, I tried this excursion out for something different. It starts with a half hour boat ride to a private beach where you can snorkel, rent waverunners, or just sunbathe. While your on the boat, there is unlimited rum punch served and a small band playing calypso music. Everyone in our group had a blast on this excursion, and I believe it was reasonably priced (around $25 a few years ago).
We did not snorkel, and I cannot recall if they had gear available for rental. However, I wouldn't recommend this excursion if you are looking for good snorkeling. This was more of a beach party atmosphere, with the rum punch, live music, and dancing. I've heard of better places in Nassau you can go if snorkeling is what you are looking for (although the names of those excursions escape me). Hopefully, someone out there knows where the good snorkeling is in Nassau.