I use PRICELINE all the time for San Antonio - I usually bid on a resort in the West area - Seaworld and have gotten more than once the Hyatt Hill Country Resort for $42.00/night - talk about a bargain - that place is usually $250.00+/night. (I do go in the off season too which may be why I can get such a low rate)
I see people getting nice hotels on the Riverwalk all the time a lot cheaper than booking directly with the hotel.