Bikes that need a lot of work and parts are best suited for people that are ready and able to do the work themselves. If you pay someone to do the work, you will rapidly exceed the value of the bike.
+1 Donor bikes are the solution to getting a lot of parts for not much money. I usually find donors in the $5 to $25 range.
The key to any project bike is the condition of the frame. It the paint is bad, if the frame has dents and dings, if there is serious rust, at that point, the bike has become a donor. Unless it is a very collectable high end bike, dealing with those issues can cost more than it is worth. Minor rust can be taken care of if you are handy.