I would trust this more than what people on this forum are going to tell you:
http://www.bostonpinball.biz/eBay052910.htm
Especially on a high production game with lots of sales like Black Hole.
My personal opinion... no way in hell I would pay $650 for it unless it was in amazing condition and totally complete with the exception of the MPU. With it unshopped and missing the MPU you're going to have trouble recovering your money. Worst case is you'll be into the game for several hundred more than it's worth.
At the end of the day $650 isn't a huge sum. If you are dieing for a Black Hole and this is the only one you expect to see locally then go for it but at least try to get the price down. Who knows... the guy might give you a good deal if you ask.