Get an idea what that model was new and go from there. Couple things to consider is what options the trailer has, how much use has it seen (nights versus miles), where has it been stored when not in use, what is included with trailer (what is included knocks down the the additional cost of what you might need) and overall condition. Most that come up appear to be in great condition so you are probably looking at what did it cost new then maybe minus a percentage. Seems most have gone for a fair price that I have seen.