If your shotgun has good wood and blueing,then the Winchester model 12 shotgun will bring between 275-450 dollars on today,s market.The gauge of the shotgun helps also with the 12 gauge being the most prevalant,and the 16 gauge and 20 gauge being produced a lot less,hence more value.
To determine the exact value of a CG Bonehill 12 gauge shotgun a couple different things would need to be taken into consideration. Some of these things would include the age and condition of the shotgun.
To determine exact value of a 1904 Marlin 12 gauge pump shotgun, you would actually have to take a number of factors into consideration. The main thing to consider would be the condition of the shotgun.
The value of ANY firearm is based on the exact make, model and condition, You did not give us enough information (serial number provides none of the 3 items we need). Eastern Arms was a brand name used by Savage for guns sold mainly by Sears. Value in good condition is likely around $100.