It's going to be painful to do this...but I'll bite my lip and try.
Cab: Free (local distributor) ~$100 value
Monitor: Free (paid for by my company in trade for building them a cab) $250 value
Computer: Free (same reason as above) $500 value
Controls: (2 Perfect 360s, 4-way stick, buttons, spinner, trackball) ~$250
LEDs, Wire, Solder, tools, paint, etc.: ~$200
Control Panel box: $100
Speakers: $50 (I kinda went overboard)
Marquee light and marquee: $50
T-molding, panel art: $25
Misc. other costs: ~$75
My approximate cost: $750
My approximate value: $1600
The cost is pretty high since it was my first time and you make a lot of mistakes...some that drive up the price. I threw in a pretty nice computer and TV set (27" via component connection).
All in all, it's been WAY MORE than worth it. The first time my wife absolutely lit up when she beat me at Puzzle Bobble made it seem like a bargain.