We stayed one night at Hostel Soberanis in downtown Cancun in June. It was very easy to get a reservation through the internet, it was cheap, about $40usd, clean, comfortable, it had AC, TV and continental breakfast included. The staff was helpful and friendly, they recommended us a good italian restaurant nearby. It's a fair hike from the bus station, and be prepared for lots of solicitation from other hotels, but it's do-able to walk. Besides, taking a taxi is highway robbery. Breakfast was fine, coffee good and hot, danishes fresh. This was our only sighting of cockroaches, albeit small ones, and only two. (Face it, most of the restaurants in the US have them too.) We would recommend it for short stays.