Well the website for neo is
www.neo-geo.com. Great site with lots of smart people and a MASSIVE message board that answers any question you may have (someone has already asked it, I am sure).
I just kind of blindly took the plunge and bought a Neo from a guy in the next state. I drove about 2 hours in my full sized pickup, had him wiggle it to the bed and threw it in. Be sure when you go and pick one up to tightly strap it down. Most people are going to lay them down if they are buying one game and have a truck.. what you don't want is some sliding around in your bed.. because if it slides the rear glass of your truck cab you've got a broken window, just FYI.
My MVS is an original, which I would definetly recommend over a conversion. You see, a cab is pretty much a cab and you can convert any old cab to whatever game you want (I mean, you can't get one of those crazy skiing games into a standup cab, but...). The bonus of an original cab is that it will have the right button placements (the A button lower than B, C, D) the game-switch button (if you have a 2, 4 or 6 slot) the lighted marquees, etc...
Oh yeah, the multi-slots. My MVS is a 4 slot and works great. Some older 1 slots won't play the very newest games (post SNK, released by Playmore). I think there are some hefty power requirements for a 6-slot and they are known to be a little flakier than the 2 and 4 slot machines, fyi.
I paid about $400 for my MVS, cash. You can get them much cheaper if you go to an auction (Super Auctions) but you can't be sure what you're going to get. They aren't super complex machines to repair and the neo-geo.com boards are a tremendous resource but I am not electrically inclined so I was willing to pay a premium for a fully functioning system. You can get one in a converted cab with like a crummy 19" monitor for $200 on ebay, and I would expect to pay about $400 for one in decent shape.
E-Bay is your best for the MVS carts. You can get the most popular Neo games for cheap, Samurai Shodown will run you $10, most of the King of Fighter line is $10 a piece... rarer games can fetch $200 or more if in kit form. There are a few sites that sell new and used carts online, but eBay is the biggest market...
I could ramble on a lot longer.. but I'll leave it at that for now...
My Neo when I got it home...
Slightly cleaned up...