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.