Someone asked for an approximate cost rundown, so here's my best effort.
Cabinet: $35 off craigslist, but renting a truck to move it brought the cost to more like $100.
Lumber for building the inside supports/shelving: $0 Acquired free from wood being thrown out at home construction site down the street. At least I think it was being thrown out. That's my story and I'm sticking to it.
Controls: $200 Xarcade Tankstick
http://www.xgaming.com/ Worth every penny. Can't say enough good things about this. Yay trackball!
Marquee Light: $10 florescent work light from Home Depot. Simple and works.
Marquee: Haven't bought this yet, but it will be somewhere around 30 bucks for good quality stuff.
Speakers: $20 Logitech speakers from Fry's Electronics
TV monitor: $80 25 inch TV off Craigslist - most important thing was having a TV with a S-Video output. I did not decase the TV screen.
Computer system: I probably spent about $300 dollars on this not including a video card (which I already had laying around - again, S-Video input is key) which is more than you have to. I have way more power in the computer than I need, but maybe someday I'll consider putting some PC games on it and playing them through the arcade as well.
Surge Protector: $30
Smartstrip off of Amazon.com Very key component, as it allowed me to power up everything by just the push of one button. Incidentally, if I had Windows Vista I could have set everything to turn on with a button press on the controller deck. I don't, and the TV remote is fine for me.
Paint: Probably somewhere around $150 total for all the cosmetic work, including Primer, Latex Paint, brushes, rollers, spraypaint, clear coat, plastic drop to protect the back porch, painters tape, wood putty to repair damage, an electric palm sander, and sandpaper. Again, we spent more on this than is necessary, but we wanted it to look great, and we couldn't be happier with how it turned out.
Hardware: Maybe around $30. A wide assortment of nuts, bolts, and screws. The casters where the most expensive hardware - maybe 20 bucks for the set of 4. I was able to reuse some of the inner components when stripping down the inside of the cabinet. I have leftovers here for other projects.
So everything I listed is a little over 900 and I tried to estimate high. I'm sure there's probably little stuff I'm forgetting. And then there's the cost of gas. So figure maybe 1000 bucks tops. You can definitely do it for less if you find deals on stuff (reuse and old computer, find someone giving away a cabinet) or if you're happy with just a quick spraypaint job for the exterior you can save money there.
Hardest part: Definitely trying to get the shelf for the TV in exactly the right spot. That thing is VERY heavy, and just prior to that part of the construction, girlfriend injured her knee making her unable to help with lifting/holding in place, etc. I'm very pleased we were able to get it as well as can be got.
Most fun part: The day I set the controller deck in place prior to all the main construction and seeing it fit so well made me realize "Hot damn! This is actually going to work!"
Now I'm off to go play some fighting games. I'll decide which one on a whim.