If you are just going to have one cabinet, and have no tools to start off, just buy the complete Ultimate Arcade II kit from mameroom. You'll put it together really fast and the results will be very good. I spent a lot of money on tools when I built my first cab (much more than I expected).
At a MINIMUM you will spend $60-$75 on wood. $5 on glue, $5 on screws, $150 on cheap tools (cheap router and slot cutting bit, drill, circular saw, jigsaw), $25 on paint and supplies (sandpaper, roller, primer, paint). Then there is the time you will have to spend on doing all of this. Don't get me wrong, it's great fun and you will learn a lot, but it is very time consuming.
Good luck!