I found a deal at lastminutetravel.com. They have a 4 star hotel on Isla Mujeres for $48.14 per night, the catch is you don't know which hotel it is until you purchase. It also did not say if it was on North Beach or not.
It has the following amenities:
Non Smoking Rooms
Wheel Chair Access
Restaurant? Elevator?? Privlege Aluxus is the only resort that come to mind with all of these features but I am not familiar resorts on the south end of the island.
Does anyone know of another hotel with these amenities on Isla?