This can help you find it's age.
http://ismacs.net/singer_sewing_mach...-database.html
Markets can vary wildly from one region to another. Try watching Craig's List in your area for a little while. That will at least give you an idea of asking prices on similar machines. Just keep in mind asking and selling prices are two different things. Completed sales on Ebay can give you a range too. Ebay prices tend to be higher than local sale prices.
Rodney