Am I missing something?
Yes, you are. Here's a cost breakdown of my very first Mame cab:
Cab - free, off Craigslist
Computer\Monitor - free off Craigslist
Blood, sweat, tears - also free, courtesy of me
Keywiz\Joysticks\Buttons - $75
Misc scrap wood, screws, etc - ~$25
$100 total.