Mike, I paid $400 for my freshly rebuilt 355. The thing lasted 5 years in my truck (I sold it to a friend to finance my 454, but it is still runnin strong) and never once even leaked or burned a drop of oil. For performance's sake, it had two different cams, one additional set of rockers, two additional intakes, and I upgraded the heads once. It also went to the 1/4 mile track 75 miles away, raced it 13 times that day, and drove it home. I also had it in two burn-out contest at the Car Craft Summer Nationals, and it saw the other side of 100 a few times.
Good deals can be had, but you still have to be very careful and be able to tell if it is TOO good of a deal.
-Jeff