Looks like a pretty good deal to me, more or less of a good deal depending on whether the front glass is included and whether you plan on keeping the marquee and side art(if present). For comparison, I obtained a MK2 cab for free. The sides had been painted black. It did not include the CP, monitor, or glass. It cost me $20-30 to strip the paint from the sides and luckily the side-art is in great shape. I still need to find a TV to put in it, probably another $30. The front glass will cost me about $80. Spent $20+ on a slot cutting bit and a forstner's bit for the CP. Still need to buy wood, plexi and paint to build the CP, probably another $30-40 (using a MK poster for the CP overlay). The marquee will cost ~$30. Then I also had to buy joysticks and buttons, don't know if you plan on keeping the ones that are already there.
To me, the value is dependent on how much you plan on keeping and how much you plan on changing out. If the monitor works and the front glass is present then $150 is a deal.