Hotel Alux was a very good budget place. We stayed 1 night before going home and it was very close to the central bus station. The staff in the reception was very nice and helpful. The room was very basic but clean, and the bathroom was spotless! I would definitely stay here again for shorter periods! The price was 3 usd/ 330 pesos.

Attn tripadvisor.com: hotel's website is:

I found this hotel a great value at 30 USD per night (One person July 4-6, 2006). Cancun's bus station is right next door (with cheap & comfortable bus service to the airport!). Plenty of money exchanges, restaurants, mini-marts, and internet cafes nearby as well. There's also a self or full serve laundromat next door which I found useful.
My good-sized single room had a decent bed, good A/C, a small TV, and was in a secluded part of the hallway on the 3rd floor so it was quiet.
My only complaint would be non-movable shower head that sprayed straight to the opposite wall. Being tall, I was lucky to have the water at least spray my head.
Saving money at this conveniently-located hotel with its very friendly staff members will bring me to stay here again in the near future. Just find their website and make a simple reservation via email.