Living in Mexico was an adventurous fairytale; due to the variety of things to do, beauty of the country and the kindness of its residents. I am originally from Ohio but spent substantial time living in Mexico, studying the nature and history of this beautiful place. Here are some ideas and tips I learned from being there that may help you on your next trip to the Yucatan Peninsula.
Using the public bus system is infinitely cheaper than taking taxis everywhere. If you are looking for cheaper transportation to and from the airport, take the bus to downtown Playa del Carmen or Cancun. It is easy and the bus stations are centrally located in both cities. You can choose to ride an air-conditioned bus for a small amount more than the non air-conditioned bus. I would use either, whoever left soonest. There are bus schedules posted for local travel or throughout the country. The nicest buses when I was there were the plush tour buses for longer trips, called ADO. Really nice buses that cost more but are worth it.
If you need to make phone calls in Mexico, buy a phone card there and use them from any pay phone. They can be used to call internationally as well. The locals, many of which do not have phones in their homes, use them all the time. You can buy them in the Casas de Cambio (places where you can exchange your money into Mexican pesos). A note on exchanging your money, check around, to look for the best exchange rates as they may vary place to place.