hmm I may just opt to get a cabinet and get a mame emulator running.
A supergun is a home set up but you would still need the jamma board unless it's programmed with games.
They do sell RGB to VGA or HD cards.
I don't recommend rehabbing an old cabinet because in all reality, it could be a fire hazard and having only one game IMO is a waste of space.
Most arcade games now are computers in cabinets, you can look up Betson on their ICE machines like Fast and Furious bikes or Sno Cross, it's a Red Hat linux computer. Sadly, they need to be serviced alot due to the HD going out.
If you find an used original machine, it'll be around $250-$350 though.