The farthest back I can go is 2001. I went to my first arcade auction that year.
At the time I remember Funhouse was about $1000-$1200 in decent shape and everyone thought that was very high.

At the auction in 2001,
I distinctly remember a very nice High Speed sold for $500 and a non working Black Night went for $250.

I also remember quite a few non working arcade games selling for $20 each. Donkey Kong, Mario Bros. and Galaga for certain. There were literally 20 non working Street Fighter II arcades that no one wanted for $25 each. I bought a Crystal Castles for $100 at that auction and a working Klax for $100. I actually still own the Crystal Castles.

The first pin I bought was not until 2003 and it was a non working Jokerz! for $300 in Erie, PA. I ended up trading it for a very nice High Speed which I still own to this day.

Now, those are certainly not the best finds I've ever had but they were the FIRST finds I ever had.

About one year later I passed on a HUO Bally Spectrum for $500 because I've never heard of that game and only had room to bring back one machine. Man, I should have bought that damn game. Still haunts me to this day.