Hi, meya ...
You might want to give this link a try.
If there is an option to go to Tulum on a shoreX, that would be a much more satisfying experience, regardless of the cost. My husband and I took our own version of an achaeological expedition earlier this year and went on the ruins hunt. The ruins near Costa Maya are not in the top four or five, but are still interesting. Do NOT forget to take mosquito repellant that contains DEET. Mosquitos are the Yucatan Air Force.
It is very easy to drive in Mexico. The roads are well-marked. But a little bit of Spanish and a good map help.
You will really enjoy the Captain Marvin experience. Just make sure to take some sodas (all Marve supplies is water and some icky fruit punch) and some snack food. After a while on the water, the bait chum starts to look good. When you check in with Marvin (turn right off the tender pier, his office is in a shopping center to the left just past the Hard Rock Cafe) there's a little store there for snack foods. An Internet cafe with the world's best view is upstairs in the same building.
Tell us all about it when you get back !!!