A quick look on GB told me they are scarce & desirable, actually something I was semi aware of. You likely know that as well.
With that, I like to let a seller tell me what they want for it. If they're reasonable you can go from there. Thin ice to offer first. Ya take a chance on insulting them, or,,,, offering more than they had in mind & they tear your arm off taking your money. THat's palm smack then, gee! I could have bought it for less.
I know one thing, if you plan to shoot it, & especially if ya reload, you'll enjoy the heck out of it.