I have no idea of the current value. But I had one many years ago.
Mine had a plain crosshair reticle and provided no magnification. I remember seeing magazine ads which promoted the K1 for use as a shotgun sight for wing shooting. That was probably in the 1960s, way before specialized turkey and deer shotguns with optical sights became popular.
I think the K1 would be fun to have on a levergun, especially in one of the pistol calibers.