A completely MDF cab is pretty much worthless, they don't even make good firewood. The CP, marquee, JAMMA harness, coin door, bezel, and power supply are all usable (or ebayable) bits and their combined value are what the cab's actually worth.
On the other hand, $50 will buy you a complete working game at auction, I've bought three for less than that. $25 will get you your choice of several empty cabs at auction. Since they can't power it up monitors in empty cabs are assumed to be broken. (If the monitor worked, the operator would have likely pulled it to keep as a spare, or at least pulled the chassis board.) This one would end up in the last row, and would likely sell for minimum bid.