There was a '97 in the Forums classified that just sold for $19,900, but that is just one trailer and it isn't exactly the same year model. So much depends upon condition. What I can tell you is that NADA values are way too low, but for grins do a google search on NADA, then go to travel trailers and then to Airstream trailers and see what a '99 lists for. All I know is that NADA for instance shows high retail of an '89 at about $9,000 for a really, really clean one and I'm telling you I don't know where you can find such a trailer. Go on eBay and see if you can figure out anything. Search other RV sales sites. You're just a little bit late in trying to figure all this out on that particular unit I think. Sorry, I can't help you more. Maybe if nothing else, I've bumped this thread for you so someone else will see it. The problem is that on weekends, activity here drops way off from what it is during the week and you don't have that much time.
You say its priced too high. How do you know that? You didn't say you had any comparables, yet you say it is too high. I'd be way more concerned about what condition the trailer is in than I would over whether it might be priced a little too high.