I have nothing that would tell me when your gun was MADE but it bears British proof marks from the Birmingham, England proof house as used from 1925-1955. Surely in the first half of that period because they shifted from Suhl to Eckernförde to resume production after WWII.
I think it may have been originally made for sale in England because I see no German proof marks.
It is an interesting looking gun with blued dummy sideplates contrasting with the grayed receiver.
I don't have any references on prewar Sauers, sorry.
There is a collector here, Sauerfan, who has a lot of information. Maybe he will notice your post.
I don't understand the value question, though.
Unless it "came to you" by gift or inheritance, surely you paid what you thought was a fair price for it, and that is the only real way to assign a value.