$1000 to $2000.
Depends on the conditions-
The ones with the red letterings intact go for more because they comes off rather easily. A lot of them have one or two of the screws missing. Some sellers claim that you can buy the screws from Joe Grado. As far as I know he doesn't sell them (might have done in the past).
Original box and paper work can also play a part in the pricing. A very few pairs of HP1000 have been upgraded by Joe, no idea what these would go for.