There's currently a King 2280 listed by Carolina Pawn, with a starting bid of $500. I live about 10 minutes from their storefront, so since I'm looking to buy a euph, I went over to check it out.
1) based on what I saw, I will NOT be bidding on this horn, due to what it would cost to have it refurbished to a condition that I would be happy with;
2) I am by no stretch of the imagination an expert or an appraiser: I'm an amateur who's picking up the euph again after a 27 year hiatus.
With those caveats in mind, here are my comments:
From the serial number, it appears to have been made between late '78 and early '79. (The sn of my King 2268, which I bought in June '79, is 7444xx, so it's about 2600 higher.)
The horn is in fairly reasonable shape overall, but does have some dings in addition to the dents shown in the listing. (I counted about 20 dings, including one in the leadpipe (you can see it in the large version of the second photo) that probably does not affect playability, and 4-5 additional pinky fingertip size dents.) The dent in the fourth valve tuning slide, however, does affect playability and intonation, but how much is hard to say because both fourth valve slides, as well as the main tuning slide and the second and third valve slides are frozen, as are the bottom valve caps.
There is some minor wear on the valves, but they're not loose or leaky. Valve action was sticky, but that cleared up after giving them a shot of Blue Juice, however the crud under the valve caps was DISGUSTING! I initially experience a minor airlock in the first valve after oiling it, but that cleared up upon removing and reseating the valve.
Cosmetically, the silverplate is in fairly good shape. There is the usual assortment of scuffs and scratches, but none that penetrate to the brass underneath. There appears to be a 3/16" flake of silver missing from the bottom valve cap on the third valve (it could just be heavily tarnished, though a brief rubdown with my tarnish cloth didn't remove or lighten the spot), and some of the hard-to-reach spots and braces are badly tarnished.
The thumbscrew on the lyre holder is missing.
The case is in poor conditon structurally: there's about 1/2" of play or wiggle diagonally in both the body and the cover. It does latch, but the cover is racked (skewed diagonally), so you have to twist it to align the latches. I certainly would not entrust any instrument I owned to it!
The horn, however, does play well. It blows very freely (aside from the fourth valve) and has a nice, dark tone. The intonation with the slides in their current positions ranged from 32 cents high to 21 cents low. I was not able to correct the intonation due to the frozen slides. (I was also unable to test the third valve slide trigger.)
For the right price, someone could end up getting a good deal on the horn. If you can live with dings and small dents, you could probably get it reconditioned to "playing condition" for $200-300. If what I saw under the valve caps is any indication, though, it would probably be a good idea to get it chem cleaning as well.