I bought my first pinball retail in 1997 and caught the bug and started attending/buying at the coin op auctions pretty soon thereafter. My budget was usually $1000 and I would typically come home with what is considered an A list WMS/Bally most of the time.
My best story is for a brief time they started having auctions in Louisville. I talked my wife into going to one there in the middle of an ice storm about 1998 or so (I had an open bed 4WD pickup and thought I was invincible). We walked in and what was sitting there at the end of the row, a game I had only heard about but never seen - Medieval Madness. It was the first one the auctioneer had seen as well from his reaction when he got to it. The whole time I'm watching the crowd and realizing the monied folks were not there (probably because of the aforementioned storm). I looked at my wife and said that one was going home with us. I don't remember the exact amount but I think I got it for $2700.
Got it home and first thing I went to do is start replacing all the lights in the backbox because they were all out. As it turned out the operator didn't notice/bother to plug in the harness to the tub so those lights had probably never been on since they were tested at the factory. We didn't even play the game at the auction because there were so many folks around it, I had a little scare when Lord Howard Hurtz said his famous line for the first time (that gets beeped) and my wife gave me the look that said I might have to sell this one. Thank the WMS programmers for putting a family mode on that one or it would have been gone.
At other auctions I remember getting a Safecracker for $700, STTNG for $900, TZ for $900, CFTBL for $1400 I believe. Those were the days!