Yeah, pinballs have become "collectors items", right up there with Precious Moments figurines. 
And hey, a $525 pinball for $50 ain't bad, btw...
Heh, yeah. I was at a yard sale this past weekend looking for N64 games and there was an index card on a table that said something like "also available: brown couch, tan recliner, pinball" The index card was so small you could barely see it with all the stuff. I asked about it, dude had the machine in his basement and it had probably an inch of dust on it. $50, he helped me load it into my car, and his wife gave me a root beer and cookie.

On a sad note, he said he'd recently thrown away 4 (four!) arcade cabs that he'd had in his garage. "The mice got at them and built nests so I figured no one would want to clean them out." He didn't remember titles but judging from what he did recall, the only potential classic among them was Pole Position.