Original questions still stand though, any idea of what constitutes a good deal helps.

Bike <50% of intital cost if <5years old, much lower if older and or obviously ridden hard and abused.
Learn to spot where frames made out of different materials tend to fail and look for signs like cracks, bulges, and deep dings. Knowing what size frame you ride and how to fit the bike yourself, or a friend that does is nessary. It's not a deal if the bike won't fit you. If you are able to wrench your own bike it helps make a deal easier to find. I would have NO problem paying $1000 for a bike that sold for $2500 just a few years ago, especially if it wasn't raced every weekend.