I remember the old 670 Winchesters, just didn't realize they chambered it in .264 Win. Well, before Winchester went belly-up I would say that $300-$350 would be a fair price for a used 670. Now, no telling. I think I would start off offering $300 and go as high as I felt Okay with. I doubt the previous owner (owners) ever shot it enough to hurt it, and even if it had a 22" barrel ( you didn't specify) it would still be a good using rifle. Every 670 I saw was in 30.06 and plain as dirt, ha, you can't hurt a rifle like that in the field though.
I have a good friend down in Texas who bought a Mod 700 BDL from another friend of ours, way back in the late '70s, he still has it. He (and now his boys) have shot bookoo deer/hogs with it at some impressive ranges. Good luck to you Pard.