Well I have already stated that I am not the best person to assign value, but I'll give it a rough shot that you can use until someone who really knows their stuff chimes in.
First off, the value depends a lot on not just the model and year of the horn, but also on what the condition is and whether the lacquer is original or a relacquer. Even a rather well worn horn with original lacquer is worth a lot more on the market than a relaq. (This is crazy to me, but I don't make the rules). From the photo of your horn, I think it is a relaq.
The next important issue is the playing condition of the horn, and how much extra expense a buyer faces to get the horn to play well. If this horn has been recently serviced, has good pads (such that any additional service faced by a buyer would be minimal), I would estimate the value of the horn somewhere between $2K and $3K.
From your correspondence, I assume that you are not a player, and the horn has been sitting around for awhile and may need significant service to play well. A full overhaul of a horn can easily run around $1K, so that would place the horn value in the $1K to $2K range.
I know that this is a broad range, but to get any closer, one would need to inspect the horn, or at the least see a whole lot more photos. I hope that someone who is really in tune with the market jumps in and gives a better estimate for you.