itlnstln had the best advice.
Go to Hotwire, and their starting price is your "safe" price (you know you can get a hotel/motel for that price). Then go to Priceline and bid under the Hotwire price and see what you get.
I have no experience with betterbidding.com but it sounds like it could add even more clarity to the process. My experience has been that the rest of the "cheaphotels.com" type sites always fall short of Hotwire and Priceline.