For a restore bike, I prefer a steel frame, like a vintage Trek. You will see them on Craigs List frequently. I picked up a 1987 Trek 330 at Salvation Army a few months back for $18. I only wish it was a larger frame size.

If you are not in a rush, I would start going to garage sales and thrift stores. Seems like some thrift stores commonly have bikes, others never have them. And it is more common to see the Xmart junk than good name brand stuff. Garage sales can be even better. People at garage sales are often just trying to get rid of stuff.