Oh, a couple of other things....Cozumel is not expensive compared to many other places you could jump to from Florida and the dollar gets you a lot of pesos now, at or near historic levels. I wouldn't pass up this opportunity.
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If you have any interest in Mayan ruins, then you need to modify your plans. Some of the greatest ruins in all the Americas are within a few hours drive of Playa del Carmen. There's a tiny ruin on Cozumel, but you won't be impressed. Chichen Itza is impressive. The problem with Chichen Itza is that it's overrun with crowds of idiots during the mid-day...because it's within driving distance of mega-resorts in Cancun and all along the coast. You do not want to be there from 11 am to 3 pm when the crowds are at their peak (coincidentally, when the day's heat and sun are at their peak, too). Fix that by arriving near the ruins late afternoon - go for a couple hours before sunset (after all the crowds have gone back to their cruise ships and mega-hotels). Spend the night at one of the hotels right by the ruins. Wake up early and go in when they open. Enjoy a few more hours with no crowds. Then when all the buses roll up, leave.
When I did Chichen Itza, we took a tour by air. Left Playa del Carmen early in the morning in a small airplane, and landed at Chichen Itza shortly thereafter after a brief fly-over tour. . . .
Wowee, that must not have been cheap. I took a public bus out to Chichen Itza. I don't think I hired a guide, and I probably learned about 1/1000th of what you must have learned about the site.