What a beautiful machine! In central Mississippi (where I was living) folks would ask about $200 for it but would likely get $100 for it. Since the owner doesn't know if it still works, offer the price you think is fair and plan on fixing it yourself. It is a gorgeous machine and cabinet! If the top of the cabinent is scuffed up, that might cause you to want to lower your offering price but it all depends on how much you want a machine with those beautiful decals in place. The case can be stripped and revamped much easier than finding a machine with gorgeous decals.
Try looking in facebook marketplace for your part of the world to find out the going prices for machines. Bottom line, what is the machine worth to you? I would buy it for $100 :-).