If you want to do a three day dive package, you should go with Playascuba.com. They have a package that is 200$ (american) for three days of diving, Two Playa ocean dives, Two Cozumel Ocean Dives and Two Cenote Dives. Its really nice if you havn't done to much diving in the area because you get to have a little taste test of a few different places.
Playa scuba, super good guys. I dove with them a lot. The two guys running the show and doing all the dives also own the shop so its very personal service. Super good rates, Really nice gear. Overall really nice experiance.