1985 honda atc 250r for sale

I have a 1985 Honda ATC 250R 3 wheeler that I am considering selling, but I need some help on a fair asking price. I am the original owner, bought in May 1987, brand new from the dealer. This bike has always been garaged and I would say 95% of the time used in the sand, never raced, all stock, with the exception of an added speedometer/odometer (my best estimate on mileage on this bike is less than 1000). My wife was the main rider, although after I sold my 350X I used this one periodically. It has been sitting in the garage since....