If the financial portion is too much of a burden then (sorry BYOAC, I MUST say this) are you sure this is the right hobby for you?
With that out of the way, if you've answered yes, then you have a classic A, B, C problem where you can pick two of the three. They are:
Cheap
Fast
Good (or well for the grammar police

)
Therfor.....
If you want it cheap and fast, it's not going to be good.
If you want it cheap and good, it's not going to be done fast.
If you want it done fast and good, it's not going to be cheap.
Since money is an issue, that precludes option #3 and since you want a nice cab (I assume) then #1 is out. That leaves you #2.
Divide your cab into modular components that you can work on. You kind of hint at it in your post but you're focusing on the most expensive rather than the cheapest. So.... Software is super cheap, so work on your MAME configuration and front end. You already have your CP parts so you can spend time hashing out your layouts and experimenting to see which layout you like.
Meanwhile, for the parts that cost the penny, figure out ways to get that cash. Sell blood, work a second or side job, ask for overtime. Reduce your bills. Things like is TV really that important? How about that Starbucks? Taco Bell/McDonalds/Whatever? Girlfriends/boyfriends/gayfriends are iffy. Do you like sex or gaming more? Do you really need that college education? What about those toys you never play with anymore? Do you really need furniture? (Note: For a long time I only had three pieces of furniture. Couch, computer desk and entertainment center. I did have a bed at one time but... long story, never mind. I actually did not need anything else.) Sock that money away until you have enough to buy the parts. And as always.... watch for those deals wherever you can find them. Craigslist. Ebay. Whatever. Don't just look for the deals that go directly towards your cab but look for the ones you can part out and sell. I got funds for my first cab by obtaining a whole slew of cheap and free cabs to which I parted out and sold on eBay. Be careful what parts you pick up though. I have a fiberglass racer seat that I paid for that absolutely
no one wants and because the economy took a ---steaming pile of meadow muffin---, it's far easier to find the craptastic "Perfect $1800 MAME cabs" than the cabs from people just quitting the hobby or business.
Three of my biggest projects were put on the back burner because I decided to have kids. Go figure. Now I can't bring them "forward," not because of money per se, but because my wife insists on having "furniture." Why the ---fudgesicle--- do we need a dining room table?! Nobody ever eats at it.
