If you decide that you want a cabinet, an X-Arcade typically isn't a good place to start, as Donkbaca may now be realizing.
I find this insulting. I am doing just fine with using an x-arcade as my start. Got many good years out if it and it now lives on as the guts to my new CP. Even if I didn't decide to gut the thing I could have sold it on e-bay and gotten just about what I put into it. Sure the x-arcade encoder is a little different since it doesn't have a common ground, and the wires are a little short, but extending wires isn't at all difficult, and the encoder works just fine.
There is nothing wrong with an x-arcade. The kid is 18, he doesn't have fond memories of the wonders of leaf switch buttons and joysticks that people on this forum go nuts over. The arcade cabs in his memory are more likely Neo geo multi slots, dynamo cabs and crappy conversions on beat up old cabs. Most, scratch that ALL of my friends that aren't hard core arcade nerds think the x-arcade is great.
Going cheap is pretty much near impossible. Unless you have a free pc, a free monitor and a free cab, and already have all the tools, its pretty hard to keep a 2 player build under 200 bucks unless you get really lucky. Add up the minimum cost, people always leave stuff out, because they have stuff laying around. The kid is 18, he probably doesn't have a woodshop at his disposal.
Look I don't want to be negative, and if you really want to build a cab, I am all for it, but lets not pretend like its something that will be cheap and easy. Maybe this kids situation is different than that of mine and my friends, but anything over 200 -300 bucks is a lot of money to a kid that age, and he could invest in an x-arcade off ebay, and a external hard drive and try out everything. If he really digs it, he can either gut the x-arcade or resell it for probably what he put in for it, plus or minus 20 bucks. He could plug his external right in to his dedicated cab and use it, or transfer it all over.
If he decides it isn't worth it to build a cab, he can still play his games.
If he decides its a passing fad, and not as cool as he thought, he can ebay the x-arcade as mentioned and either keep the external hd, they are always useful to have around, or wipe and ebay that too.
To me that makes a lot more sense then buying a cab, dumping a bunch of money and then potentially being stuck with a cab that there is no way he will be able to make his money back on.
Not to mention the opportunity cost of that money.