I've got something cheaper, although it's still a Mame solution...
Get yourself a Delhi III motherboard. They came in eMachines. On eBay all the time.
There are DOS drivers for the sound, and there are onboard ATI graphics with non-shared memory.
Get a 16M flash card, with an IDE flash reader. Set up DOS on it, with the sound drivers, and have it boot right to Mame and Galaga.
This board runs Galaga @ full FPS with a 450 MHz processor. And with .96u3 it's darned close to the real thing. In fact, with the newest version I'm not sure what the difference is between Mame and a real board.