The funny part is that a lot of people get into this hobby because they want to make something useful out of an old useless computer.

The driving cab started with a $50 empty shell, but I ended up with around $700 in it, not including the new CP with happ ffb.
I quit keeping track after it was initially "complete"
I built a 3/4 scale cab using a ping pong table found in the neighbor's trash for the wood. It ran an ancient computer and crt monitor that I got for free.
Ended up with $50 in that one, but I had a lot of oddball stuff laying around that most people wouldn't.
It actually looked pretty good for being made out of trash and thrown together quickly,
http://forum.arcadecontrols.com/index.php?topic=111821.0 My primary setup is just an x-arcade tankstick, budget pc build, 32" crt tv, & some old act labs s-video light guns.
Even that adds up to more than $500 and there's not even a cab there!

:'(
I also have piles of parts that I bought just to tinker with, knowing they'd probably never be used in a cab.
(various joysticks, positional guns, steering wheels, pc joysticks, optical encoders, aim-trak, recoil gun, 4 player cp, etc)
I enjoy learning how they work, getting them to work, then deciding if they are worth incorporating into a future cab.
Someday I might throw all the leftovers in one CP for the ultimate Frankenpanel.
Then I'll list it on ebay for a crazy price nobody would ever pay.

I'm not keeping track of what's being spent on the new cab. I usually nickle and dime it, spending around $40-50 per week.
When I do spring for a bigger order or an expensive part, I won't buy anything for a couple weeks after that.
It doesn't really feel like I'm spending a lot, but I'm sure it will end up costing well over $1,000.
I view it as a series of smaller projects that will eventually come together.
This is one of my hobbies. I don't watch much tv.
If I weren't spending money on this, I'd be spending it on some other way to entertain myself.
I'm a compulsive tinkerer with a desk job.
If I don't spend a good amount of my free time building
something, I feel frustrated.

This hobby is a nice culmination of different skills.