If you are looking for an economical way to get to Mexico consider the Yucatan Express. This is a new company sailing from Tampa. Thier twist is you can take your car. It is mondo cheap and the Economy cabins are more like train sleeper cars with a shared bath but for value it can not be beat.
For reviews you can go to Cozumel My Cozumel and look in the "getting there" section or do a Google search for Yucatan Express reviews.