Have you gotten to see this yet?
I'd say you have an equal chance of the monitor, hard drive, or power supply being the issue.
$200 is a pretty good price if you like the game and it's in a decent cabinet (especially if it's in a dedicated cabinet with full side-art). It could even be that some of the wiring is just unplugged somewhere (there are a LOT of molex connectors in mine).
The hard drive is easily replaceable ($25 on eBay), monitor probably just needs a cap kit ($10 if you can solder well), and a replacement power supply shouldn't be that hard to track down ($60 tops if you buy a new one from Happ). Another thing with the power supply is that the voltage may just need an adjustment. Then again the game PCB might be shot. It's a bit of a gamble no matter what, but you should be able to get it going.
I can check the dedicated cabinet I have in storage for the power supply if you need me to. Just send me a PM. I can even take some pictures but mine is currently missing the monitor and control panel.