From doing some research on CM, it sounds like there are some snorkeling excursions that you can pick up at the end of the pier for around $25. These were not pre-booked excursions. They had good reviews from the people on the boards. There are some Destination boards that you can find info on.
I have heard some bad reviews about the Uvero Beach excursions and the beach. The beach water is very full of sea grass. It is a 30 min. bus ride. And the drinks that are included in the excursions are watered down.
Tapas Bar is about 1 1/2 miles from the port. $3 pp one way. Chair rental $3. The food is really good, especially the salsa. Beer $2 and good drinks as well. Bathrooms are not good. You can rent snorkel equipment and wave runners. You can charter a boat for snorkeling from here. 30 min massages for $20. I believe there is no "admission charge" if you order something. They'll ask for a few bucks if you don't.
Maj. Beach-I'm sure you've seen the full spelling!!! 2 miles down the road. Again, $3 pp per way. Nice Bathrooms, wave runners and snorkeling tours available.
Tequila Beach-I believe this is apart of Maj. Beach, I'm not positive. Again, snorkeling and wave runners, supposedly an open-bar deal for $35, $5 for non alcoholic.
From what I have read, Maj. Beach is much nicer than Uvero Beach.