HI Jason,
Congrats on the cool find, What you have is a signal lock from the former Nashville Chattanooga & St Louis Railroad. Here is a link to their history: http://en.wikipedia.org/wiki/Nashville, … St.Louis
Going out on a limb, I’d say the lock dates from about 1885-1910, based upon it’s costruction.
Price is hard to determine due to what a paticular person’s intrests are. As a rough idea: If this lock was from a defunct railroad in my neck of the woods, with original key, and I wanted it, my wallet would open enough to allow 80-100 George Washingtons to escape.
Hope this helps some - Take care
–Vince
