That´s Coconuts all rigth!
Renting a car is like everywhere, driver´s license and a credit card/deposit will do. Get off the boat, rent a car and head south, you´ll hit Punta Sur in half an hour or so.
Listen friend, forget about horror stories about Mexican cops,and what the media shows you, you really have to make an effort to be arrested here, you´d have to steal, get caught with drugs or murder someone. Forget about wearing a seatbelt if you wish (In the mainland they´ll stop you for this), and just have fun, no cop is gonna bother you, I´ve even seen American tourists joking with patroling soldiers on the other side. The horrible things we see in the news happen in some hotspots. Not in all my life (I´m 47) have I seen a shootout, being kidnapped or whatever. Most of these things happen to ppl involved in things we are not, and near to the border, or very macho states like Guerrero, where Acapulco is, and Michoacán, where weed is grown and generally ugly hollywood mexican types are. Cozumel is a safe place,as all Yucatán peninsula, and most of Mexico. There is a problem here and there once in a while, like any other place in the world.
If you want to try SCUBA I´ll be happy to help, your wife can snorkel, with a divemaster, while you dive 25 fet below her with an instructor.
As a matter of fact most of my neighbours are retired Amricans, Canadians and Europeans, life is good here, not complicated, and very safe. They live here for a reason.
Come here, enjoy and be happy.
What do you think about this Bayliner for 11,000$US BTW? We have choppy waters.
http://vehiculo.mercadolibre.com.mx/MLM-424538224-lancha-bayliner-para-7-pasajeros-_JM
Cheers, Alex