I've only seen one Rottweil in person, and it was nice. I know they make some higher end shotguns, mainly for trap shooters, easily into the thousands-plus price range.
I'm not familiar with the "Field Supreme", but I'd have to think that any Rottweil in good shape, even more of a base model, has to be worth $500.
I hope somebody else can give you more specific info, but if I was in the market, and it's a nice gun, I think I'd have to buy it at $500...