Hmmmmmm, some here may disagree, but I see 3 problems with what you are looking for:
1) You want cheap, and mostly working....good luck

, from my experience, you will have to find someone who doesn't know what they have (not uncommon), and con them out of a working unit. Anyone who knows what they have, and it works, won't let it go for cheap.
2) Although the older pins are "classics", and I wouldn't chop one up, they will have less digital electronics, and more old fashioned solid-state (no circuit boards).
May want to look into that (pre 1978)
3) If you don't know much about pins, you might want to hold off. From my experience, pins are more complex than arcade games (depends on who you ask), but I've worked on both, and I prefer arcades. For example....If I wanted to modify, and trick out a '65 Corvette, I would be the LAST person to do it, cause I don't know squat about cars, and would hate to ruin a piece of "art".
Hope this doesn't discourage you, but please be sure what you are dong before you hack a pinball...you will hate yourself if you don't...here is a good link for buy/sell...I've used them before, with good luck.
http://www.xmission.com/~daina/classified/index.htmlI got a 1976 Mars Trek (a little older than what you are looking for) for $100, mint condition...someone was selling, didn't know what they had.....good luck!