these are very hard to get info on, made in England from way back, search the net for a book on them.
Try e-gunparts.com
Assuming you mean a top break shotgun, there were several models, prices will vary. For a single barreled top break, about $70-$75
suggest you contact: wellsfargohistory.com for shotgun history/value
what is the value of a Ithaca 12 ga shotgun
Mossberg
Whats the valve of a Stevens model95 12ga shotgun
Turn of the century, inexpensive arm.
100-300
how much is a steven's 12ga model 770 shotgun made by savage arms corp worth?
I own a Browning A5, 12ga,Japan made shotgun, ser: 04078. what is it worth?
Marlin
a is for 12ga and the g is for gamester