I actually started to put $350 as the lower end but hated to look too pessimistic. Should you use rifle scope on shotgun? find answers here
Another big part of it is how fast do you want to sell it ? You might hang onto it for months, bumping the ad weekly and you might get towards the higher end. Maybe.
JJ, I love those old 1100 magnums. I've owned a couple of them over the years. I just don't use a magnum shotgun anymore.
About the only thing I use a shotgun anymore for is dove and quail.