That is a nice machine, but not worth $575. $350 is not a lowball offer. It is a realistic offer in the real world, but the guy may not be in Kansas if you know what I mean.
The nice thing about that machine, is that you could move the guns to side holsters, split the monitor input cable to be the monitor for the jamma setup and a pc, and populate control panel and add mame pc into the machine. That would be a kick butt machine and economical since you would be buying the whole cab and fully functional gun game at the same time.
Oh and FYI, a police trainer board on ebay goes for about $100. So technically, you are getting a stock, no game dynamo cabinet worth no more than $200 and a $100 game. If you look at it that way you can see why $300-$350 is not a lowball.