It's all about the grade and condition with the Model 12. I'd recommend that you contact an expert on those guns. One of those experts is Stu Wright. He owns the "Model 12 Shop" and has worked with those guns for years. You can reach him at wrightsinc@gmailcom or at 618.357.8933.
If you have some pictures or can take some of that gun, I'd recommend that you do that and send them to him, so that he can take a look at it and be better able to give you a value.
I hope that helps.
"If he's out of range, it just means that he has another day and so do you."