It sounds all right to me, assuming the stove is in good condition. Does it have wear on the draft controls, or door gasket damage? Door hinges and latch okay? I think those had firebrick in the bottom, if so, be sure it is in good shape.
I don't know the retail price of that stove, or if it is still being made, but it was a quality stove when new, and undoubtedly sold for more than $500. Compared to new prices of any quality stove now, that is reasonable, IMHO.
Long ago, I built a copy of a Papa Bear stove, and it gave us good service for many years, but I wouldn't build another for $500! Twice that would be closer to the price, considering how much work it is, even with my commercial shop. Fisher used heavy material, so just the steel cost is pretty high. I think mine weighed in around 300 lbs., having ,made it a bit thicker in places, and steel plate costs me around 80 cents/pound now, so that is near half of the $500 asking price.