I love this hobby. Never have I been able to have so much fun for so little cash. This hobby also rewards you well for scavanging old wood scraps & hardware piles and being inventive!
You wanna spend some bucks, try R/C cars! I spent well over $3000 one summer on R/C racing and haven't touched those things in 10 months at best.
Seriously, unless you go hog wild, wood is cheap, PC stuff these days (especially MAME quality) isn't too bad, and you can slap together a nice CP for $100.
So far, my expense report looks like... (amounts rounded up)
Empty and stripped PolePos shell - Free
Project Arcade Book - $20.00
PolePos marquee and glass monotor bezel (and unused dash panel, shifter, wheel, optical board and pedal) - $60.00 (ebay)
Used coin door - $40.00 (ebay)
Wood, Paint and Connectors - $100.00 (and that's being generous!)
MAME PC (Athlon XP 2000, 40Gb, 256 DDR, Radeon 7200) - $250.00
Monitor (KDS 21 inch) - $100.00
CP (2 P360 sticks, 17 buttons, wires, IPAC) - $120.00
Emus and ROMS - Free
All in all, I'm into my cab for about $700.00. If I'd just made my own marquee and bezel, used my old PC and monitor and gone with cheaper sticks I could easily take almost $400 of that off!!
I figure before I finish with this cab I'll spend at least another few hundred tho on just trimmings... new t molding, better input devices, ect ect.
Where this hobby gets expensive is classic arcade parts, custom graphics and big, new monitors. =)