In my opinion, the most important thing to get in a car is a good rust free body and frame. When checking out cars, crawl under there and check every inch of the car and be wary of new paint, go over it with a magnet to see if there is lots of bondo in there.
After finding a good body, the next most important thing to me is that the car is complete. It is best if the car is at least running, but if you at least have all of the parts you have a good start.
As far as finding a car, trader magazines are good, but too many people in there know how much their car is worth than tack on an extra couple thousand bucks. The best place to find a good priced car is to look in the classified ads in the paper. It may take some time to find a good one, but they usually go a lot cheaper than from dealers. you can also check shows, sometimes there is a motivated seller. I found my car in the Washington Post, but it took months to find.