I'm in the middle of restoring a Pinbot now. Regarding price: As always, it depends on what your expectations are. If you're one of those guys who wants things to be nice, then that's one thing. If you just like to play pinball, that's another. So the idea of whether it might be "worth" $900 might be totally irrelevant to you, if it's simply too worn to fit your standards.
Having said all that, I can tell you I would NOT buy that machine, because it has too much planking. Planking is one of the most difficult things to fix, should you choose to restore. I like to restore mine, so for me that's a factor. For other guys, not something they would consider.
Kind of depends on you... How is that for a non-answer? Good luck.