We took the tour from RCCL Nordic Empress last year to shark ray alley and it was just fabulous. The boat picks you up at the ship, the ride was beautiful through the cayes. The snorkeling was the highlight of our trip. No, we didn't see a shark, but someone inour group did. The coral and fish were awesome. We had lunch back at an open bar in San Pedro, it was good and the view was fabulous. We had about an hour to walk the dirt streets and found some local merchants carving wood and making beaded jewlery. I love to buy these things that I see being made by the locals. I too thought it was a little pricey but it was absolutely fantastic and I would do it again in a hearbeat.
Hope you enjoy it!!