These are my most expensive & cheapest by monetary value only, which does not account for other factors. At the time of purchase, all titles were brand new and sealed.
PS1: 'D' in long box case - $95 (I spent more on that stupid game than Suikoden II), cheapest: $0 - A lot of games.
PS2: Ace Combat 5 w/flight stick - $135, cheapest: $5 - A lot of games.
XBOX: Steel Battalion - Green Button version. I think I spent about $150 on it. Cheapest: I bought Clone Wars / Tetris 2 game pack from CC for a penny.
GameCube - Phantasy Star Episode I+II - $68, cheapest: $10 or less - A lot of games.
Sega CD - Snatcher - $60, cheapest: Puggsy - $3
XBOX 360 - Ace Combat 6 w/Flightstick & Rock Band SE - $145, cheapest: $10 - A lot of games.
Sega Saturn - Panzer Dragoon Saga - $110
Neo Geo CD - Bri'kringer - $120
3DO - Neurodancer - $57, cheapest - Twisted - $2
Sega Dreamcast - Marvel Vs. Capcom 2 - $45, cheapest - $5 - A lot of games.
Nintendo Wii - SSBB - $39, cheapest: Red Steel - $10
Playstation 3 - $21 - Untold Legends Dark Kingdom, cheapest: God Father Don Edition - $10
Sony PSP - GTA LCS - $54 (I bought it when I got my original fat PSP), cheapest: A lot of games for $10 and less.
I have Philips CDI games and PC games (over 500), but I don't keep records of those. I might have some other random junk around here, but I didn't keep any other records in an Excel sheet.