I got some info out of that place tonight. Their response is pretty quick in e-mail.
Here are some prices
Super Converting Mother Board - $110
PS2 Kit - $20
Gamecube Kit - $25
Dreamcast Kit - $20
Xbox kit - $40
Then there are prices for the various guns and wheels.
Also it looks like if the game isn't in eeprom, then you can set it to some sort of timing mode for a game that isn't recognized. This might be an ok solution. It would be great if someone could figure out how to program the eeprom to do something that's more flexible. I've looked at the pics, and I'm wondering, if you got the GC kit, and wired up the controller input correctly, why would you need a PS2 or Xbox kit at all? I'm hoping my theory is correct. Cuz then you could just rewire it so that you're plugging an RGB signal in rather than component. If you can do that, then you can hook up any system.