Im just guessing here as you have not shown but a couple proof markings on the barrel or any information as to names or wording that it carries . It will carry those . Even the locks will be marked .
But judging from the locks , the bolsters , , TG and cheek plate I would say around 1860 give or take .
It could be earlier as back actions were in use by the mid 1830�s . but it carries a long tanged standing breech and scrolled TG . Those are late attributes
But the case could also be made that its much later in around 1880 .
What was it worth new , well guns are one of those things that�s stayed rather relative in that a rifle of reasonable quality was still costing a working man around 1 months pay . Shotguns some what less depending on the maker . High end piece could cost a whole lot more then that .
So if you figure that in 1860 a laborer would have made just shy of 6.00 for a 60 hour week , then in theory your looking at an original cost of 12.00-24.00