Too many dealers are pricing basic guns like this to sell to the likes of Bill Gates or the Sultan of Brunei. Indulging them just encourages this practice.
I won't buy any nickeled gun, but even if I would, I wouldn't pay over $450 for one, especially without the box, papers, and acc. That also applies to what I WOULD buy: blued or stainless guns.
Premium items, like .44 Magnums, might get $750 or so from me. Not being a collector or resale dealer, it doesn't bother me to buy a gun without the box, if it's in top condition. I can always put it in a nice zipper case, which I do anyway, box or no box.
I don't buy finish - challenged, rusted, or pitted guns at all. I don't have "truck guns" that are rough.
Other people do these things. I can only answer in terms of what I'd do or what I've seen. And it'd be a premium gun to get over $500 from me, not something that was meant originally as a police service gun or close to it. To me, those are $350-450 guns, and if one looks hard enough, they do turn up.
YMMV, of course.