You wouldn't happen to have a penchant for colorful sunglasses, would you?
Quick rough guestimates at materials costs as to what I'd expect to pay if I was building myself a cab from scratch with all new, quality components... This little exercise actually has me rethinking the approach I was going to take to my next project.

Wood, hardware and other materials: $200-300
Cabinet wiring, controls, electronics, lighting: $250
Barebones PC (AMD 2800+, 512mb RAM, 80GB): $300
ArcadeVGA & J-Pac: $160
Kortek 27" Monitor: $500
Artwork printing: $120
Total parts: $1530-1630
Add on a few hundred bucks for the many hours you'd be paying someone to actually build the thing...
Surely I'm leaving something out and/or have made some gross miscalculations, but I'm sure someone will correct me. Obviously there are places that money could be saved by buying used and/or shopping around as well. I went for the Kortek monitor just 'cause hey, if you're gonna do it you may as well do it right.

Personally, I'm of the opinion that if you're not looking for the whole experience of building it yourself and just want something to play, the thing to do would be to pick up a working, converted JAMMA cabinet on the cheap ($100-200-ish), add some additional buttons, plug in a PC with an ArcadeVGA and J-Pac and get to playing. It's a minimum amount of work, and would save a fortune.