"The Value of an object is what it will bring." -- legal maxim
A lot of the guys here don't do "values", in part because they can be so very subjective. I do know that I have been at this hobby for well over 50 years and, so far, I haven't sold a Snider. Sniders are too important historically..... and 'way too much fun..... to be treated as if they were merely dollars and cents.
As to determining a market value, there are any number of factors. It could, from the look of your photos, run as high as 700 of these devalued brass-plated things the Government calls "dollars", but there are any number of factors which can reduce this by as much as 500 or so of those same steel slugs. Factors include:
Lock: corrosion, rust or mechanical parts requiring replacement
Stock: has it been cut? Is the ramrod present? Any serious cracks? Is it split? What markings?
Barrel: has it been cut? Is it bright? Any pitting? Condition of the rifling? Any special markings?
A chopped stock and chopped, pitted barrel, along with a corroded lock, can reduce that from 700 down to 200 in one awful hurry. If you want a more accurate estimate, my suggestion is to post more photos, including full-length shots and at least one looking down into the action with the breech-block raised.
About 20 years ago, I was working in a shop when a huge private collection -- more than 300 guns -- came in: an estate sale on consignment..... and nothing had been cleaned in 30 years. There were at least 30 Winchester 1886s in calibres from .33 through to .50-110, all that kind of things. And there were a few Sniders. One in particular took my eye and I spent a lot of hours cleaning up that rifle. In the end, a fellow came in, looking for something 'special'. He left with that Snider, which walked out the door at $700. Outrageous price? Not really: where else are you going to find a rifle almost 140 years old....... pristine....... new...... better condition than almost ANY museum-piece..... and unfired?