I like to sit around sometimes and design different kinds of MAME cabs. One of my favorite subjects is to think up really simple kinds of cabs that can be built and replicated quickly and cheaply.
I agree that if you use items you already have or can get for free you can greatly reduce the overall cost of things, but one of the things you mentioned doesn't fit in well with what you outlined... and that is 'can be built and replicated quickly and cheaply'.
You may be able to do it cheaply, but as far as quick... unless you live someplace where you have ready access to a consistant stockpile of usable stuff people just happen to be throwing out, it could take some time gathering your materials. As far as 'replicated', I honestly can't see how a consistant pattern can be made when you are depending on scrap parts and I'd think no two cabs would look alike.
Even paint will cost you. Yes you can get Walmart brands of paint that are cheap, but they are... well, 'cheap'. People often don't realize that paint that costs a bit more is better quality and covers better, rolls smoother, and looks better in addition to lasting longer. You can go through a gallon of paint easily on a full size cab. Then you have primer. Throw in nails, screws and all the little things and it does add up.
I think you can probably make the cab itself for around the cost of the controller, and if you keep the cp to a bare basic cp with minimum sticks and buttons, even using all hacks and no ipaqs or controller boards I think it's going to cost more than you expect. I think you could throw together a quick inexpensive basic bar top for around the price you're talking but I'm not so sure about a full size nice looking cab and cp.
It will definitely be interesting and fun to see how you make out. Make sure to take plenty of detailed pics for a photo journal of your build, I'm sure many would like to see how you put this together and how it comes out.
