John Deere 420I value

I know someone that has a John Deere 420I that is all yellow. He is thinking about selling it but has no idea what it is worth. I have not seen the tractor but let's say it is in pretty good shape, what would that thing be worth? What would be the best way to sell it? I did some searching and could not find much but I did find that only 255 were made. I would imagine that tractor could be worth some money depending on the condition it is in.