The Lincoln-Pope Mercantile Company was in existance in the late 1800's, formed by Edmund Orson Pope. This was a catalog/mail order company at the turn of the century. Most likely the gun was manufactured by another company and badged with the Lincoln-Pope name.
Could be a $50 gun or could be $500. Condition is important. Advise on the following and I can give you a ballpark figure.
Steel or damascus bbls?
Dents or pits in bbls?
Hammers or hammerless?
Does it lock up tight?
If hammers, do they work?
Stock broken, cracked, shortened, altered?
Condition of buttplate and gripcap?
Chamber length?
Overall condition as per NRA guidelines?