Closer to $700 (just a little under now that I think about it).
If I'd bought a premade one I wouldn't have had the fun of making it my own.
EDIT (from another thread asking how much everyone spent):
cabinet itself - $50 (trashed Track and Field)
emdkay - $32 (Tron-style Mame marquee plus lexan)
mamemarquees - $36 (side art from bargain bin)
Divemaster - $103 (2 x Happ universals, 4 x wheels, 17 x buttons, 35ft black t-mold, pcb feet, button wrench, miniature momentary pushbutton)
Mike's Arcade - $36 (2 x coin mechs, coin door lock)
Ultimarc first order - $60 (Mini-pac with wiring harness and ground harness)
Ultimarc second order - $177 (2 x Ultrastik 360s w/balltops, 2 x medium spring, 2 x restrictors, 1 x encoder wiring)
Radio Shack, Lowes, Ace, Wal-mart - ~$100
Newegg.com - $80 (250 GB hard drive)
Total = ~$680 (my wife and I agreed on a budget of $300 )
The computer was given to me free from the local hospital. (733mhz w/ 384 MB ram)