I would buy it...
look here: http://members.aol.com/dcolucci/sn.htm
according to this list the lens is from approx 1850, which i ooold...
the focal length is easy to figure out: point the lens towards the sun and mesure the distance between the slot for the apertures and the focused sun (or another bright item far away from the lens (infinity).
that's the focal length.
(then mesure the diameter of the front lens, and divide it into the found focal length: that's the aperture..
ex: 300mm focal length. 100mm diameter of the front lens gives an aperture of F:3...)
the value is difficult to estimate as you havn't any pictures for us to see. (condition is important for collectors, so the better looking, the better price..)
that age means proberly a Petzval type lens, but that is also easy to determine if you dismantle the lenses and look for the construction...
hope this helps.
(I'd love to see it!)