Wow.
Good job in ressurecting this old thread, oldgamerz.
Well, in my case, the most I've ever paid for a game was like ¥15,000 (around US$140.00) for The King of Fighters '98: Dream Match Never Ends for the Neo Geo AES.
It wasn't anything overly expensive neither too rare, but since it is a game that holds a very special place in my heart, I will try purchaising it for as much consoles as I can.