Ignoring the money spent on tools because those aren't truly machine specific, I've probably spent $500 so far and I'm not even done with a control panel yet.  So far, that has been for the coin door, coin-door parts, controls (joysticks, buttons, trackball, spinner, etc.), plywood and lexan.  This whole machine will probably cost me around $2000 when I'm done.  I now understand why arcade cabinets that are new cost so much.
Also, I've changed my mind on my artwork.  I was going to go for a god and satan type of artwork, but I think now that I'll make a Family Guy themed cabinet.   
