Try the Hotel Alux on Uxmal, basic, clean, cheap and in a convenient location. http://www.hotelalux.com/cancun/index.htm
Cancuncanuck hit it. We have stayed here the last 3 years and it was 33 USD a night. Have yet to find a cheaper private room. Never had any troubles at this hotel. You get CTV a phone and your own bathroom and shower, it aint a 5 star (they are cleaned and sheets changed daily) but the price is right. We will be staying here again in Feb. Here is a pic of the room, we bought the coffee maker at walmart.
We always stay at Albatros Suites. It is $38 a night and has a small kitchen with a fridge and a dining table! The cooking utensils are very old and I take dish detergent to clean them before I use them. But it is a good way to have a small meal and store your cold food. No cable tv just local channels. We like the location because it is just on the outskirts of the very busy part of downtown and they have parking. It is within walking distance of Walmart and that other grocery store Cheduri(sp?). We will be there next friday night! http://www.albatroscancun.com/ Remember it is not five star but a good place to rest your head.
Thanks Susan looks like I have found a new place to stay!!! No fridge at the Alux. We used to buy a styrofoam cooler and buy ice everyday for our "fridge".