actually from the look of it, thats not actually a MAS machine. I first noticed when they said the make it themselves and are located in Colorado. MAS opperates out of California. Then I noticed that nowhere in the auction does it say MAS at all (except that they accept MAStercard).
Here's the real Mas super nova:
http://www.massystems.com/
looks like $300 plus shipping for a custom made one. I've order dreamcast joysticks from them before, placed the order over the telephone, scheduled a time for pickup but they weren't there when we had arranged, so they shipped them to me for free. I'd imagine shipping is pretty expensive, especially with 2 joys and the system. I haven't heard of anybody doing business with MAS for years, so I don't know if they are still making freshies.
I'd highly recommend
http://www.multimods.com/ but from what I last heard, Dean was having some trouble shipping on time, so I have no clue if he has time to build new projects. The two or 3 transactions I've had with him have been excellent by every stretch of the word. I've never played supergun's built by either, but it would seems that Dean's are of much higher quality build, though keep in mind joysticks are not included in his prices.