Those cabinets are premium. Otherwise, think of it this way...
Fully functional Killer Instinct in perfect condition = $800
Game board and hard drive = $150
monitor = $300
That leaves a cabinet worth $350 if it's in great condition. That's probably alot for what you want it for, but I think $100 is a great price. And those cabinets, even without sideart, are perfect-sized and solid.
Agreed, and I would probably buy one at that price (Sinner's got dibs, though) ... the only reason I am not 100% gung ho on the price is that big solid cabs with good monitors and parts have been going for under $200 at auction here recently.
At the last Starburst auction (which I missed due to my wedding anniversary

), Hit The Ice went for C$150, Virtua Fighter 2/3 for C$125, Simpsons for C$125. Granted, these were probably rather worn (but I believe they were all working ... RayB, were you there?? GGKoul?? Menace ??), but if you can pick up a working 25" monitor for an additional $25-50, that is not a bad deal ... and then you can sell the board to recoup some of that.
Now, of course, the next auction will have nothing but lousy, expensive cabinets ... that would be my luck.
Cheers.
EDIT: Having said all of that, reading the current Dreamcast thread and seeing the cool games, then looking at the 25" TV in the living room ... I realize that I really need a Dreamcast cab and that all I have to do is buy a DC, a bigger TV for the living room and one of the cabinets above.