It depends on
Field grade, deluxe grade, pigeon grade, plain barrel, polychoked, vent rib, solid rib, choke (skeet or ic much more valuable than mod or full), over all condition of the gun. Dave is pretty much right on for a field gun, plain barrel,90% condition, mod or full choke.
I saw a pigeon grade 16, ic choke, beautiful wood and vent rib at a gun show recently. Asking price was $3800.