If this is still alive, I'd have the amp checked by a competent tech, what's the retube cost and how stable is this amp-- I've owned a fair number of early ARC amps and a few preamps and other components. If the amp checks out, doesn't kill tubes and tube replacement is reasonable, the price should be Not Crazy.
I was more partial to the lower power -- 75 watt- range of ARC but that was many decades ago, when Bill Johnson was alive. Modern ARC can be good. But know what you are buying.