You can go to the Typewriter Database to find the model, and date the machine by finding the serial number and consulting the serial number chart for the brand.
As far as value, it will vary widely depending on the model, mechanical and cosmetic condition, location, seasonality, how and what venue it is sold, as well as numerous other factors. To get a general idea of the value, you can compare sold listings (not current asking prices) on eBay of the same model in similar condition. Disregard typewriters that are refurbished or sold by sellers who specialize in typewriters, as those numbers will skew much higher than the average realized price of a machine in as-found condition. This will give you an idea of the current eBay value. The local value will generally be significantly less, unless you live in certain major metropolitan areas where prices may skew higher. Hope this helps.
