Depends. If you want to build one that will play "most" games and you really don't care how bad it looks, then you could probably get away with one for under $500. However if you want to play "all" the games out there and you want it to actually look decent, then you're into the big bucks territory ($1200-$3000).
The biggest factors are:
- Computer Speed: Many of the more advanced games require faster (and more expensive) computers. However if you're just into classics this won't affect you much.
- Controls: Many of the best games used non-standard controls (spinners, Tron type stick, Ikari Warriors type twisty stick, etc). Therefore the more games you want to play the more controls you have to cram into your control panel. However most classic games just used a 4/8 way stick or a trackball.
- Monitor: Most classic games used a vertical postioned montior, but many modern games use a horizontal positioned monitor. You can either buy a very large monitor to try and get the maximum vertical space for those classic games, or you can build some kind of monitor rotating device. Both cost money. However if you're just into classics, you can probabyl get away with a nice 14" monitor in the vertical position.
Cabinet: Do you really care how the cab looks? Nice big cabs (even used ones) cost money. However you can probably get a smaller used cab cheap. If you want a big used cab, try and find a dead common 4-player game like X-Man or WWF Wrestling. They had nice large control panels with big monitors.
Hope this helps. I plan to make a MAME cab myself one day, but I'm going all custom.
Tempest