Hello Beef,
Welcome to Dave Werden's Euphonium forum.
This is starting to feel a bit like Antiques Roadshow;-) I have a question, what is the serial number? I will get you a more exact date. It is it medium shank or large shank receiver? How long have you owned it and what, if any, repairs have you had done (and where)?
Also, it is a bit hard to tell, but it seems the leadpipe is particularly dented and the brace supporting the tuning slide to the outer branch has been resoldered (somewhat poorly). These affect value.
Overall, at this point, I would put this horn at the low end of your range. While it "may" play well, it almost certainly would need work (felts, pads, corks, cleaning, polishing, leadpipe cleanup?, solder work?) that would affect value. If it were a top condition Imperial or New Standard, in top nick, the going prices are above $3K. Horns like the one that "highpitch" has that have been fully restored by top restorers (ex: McQueens in UK) go for even more. And folks who are fans of the mid-60s to mid-70s versions of these horns, often prefer the medium(euro) shank horns.
Doug
Adams E3 0.60 Sterling bell - Prototype top sprung valves
Concord Band
Winchendon Winds
Townsend Military Band