I'm a huge fan of that part of the world, particularly Cozumel. Playa is very cool also. I'd save the $250 a month and live a bit further out. Bike around as much as you can, and use the monthly savings to rent a car/scooter to travel longer distances when the need arises.
Please keep us posted as to how this goes for you! I have similar plans for when I retire (i.e., spending 3 or more months a year in Cozumel).