First let me say im clueless on this stuff , AntiPasta gave me the NeoGeo rundown on the different systems, now I ran accross this http://www.massystems.com/SuperNova.html Is this the MVS setup with a supergun? If not is this a good system?
This is just a SuperGun. You'll still need an MVS board though. These will be wired for standard Jamma, and the sticks are 6button. If you're only gonna use this with an MVS, you might wanna get an MVS specific one, with custom 4button sticks, although it depends on if you're using a single or multislot MVS. If you wanna play other arcade boards, then this will be fine. If you just want to run a 1slot MVS, you might be better off building a Supergun and consolizing the whole thing.
http://www.stalemeat.net/uberia/minigun.html Get one of these, an MVS MoBo and a standard Neo Stick/Pad. If you're unsure what MVS board to get, go here: http://hardmvs.com/html/PCBcompare.htm Oh, and I assume you have a TV with RGB Scart, or an RGB monitor. Otherwise its time for J-Rok video encoder 'fun', and added expense.
I'm not sure what you should do but don't buy a minimalist UK Supergun for $180 which still isn't sufficient for non-Europeans. I think the Super NOVA would be a better investment even though its so expensive, at least you could turn around and eBay it for cost if it doesn't work out.
Well, I could knock something up, but I can't give you a cost as it would need a decent s-video circuit and of course there's shipping. Also, I'd need to grab a 1 slot and the prices vary. Your best bet might be to ask on the neo-geo.com forums, or the Supergun Repository Forums