Stevens 12 ga, Model 77D, made before 1968 may not have a serial number. However, some do! If it has a serial number, it will be behind the trigger on the receiver side.
Based on a response that I saw on another blog - SN's were not required until 1968. The Stevens 77D was manufactured from 1940 to 1960 and therefore may not have one.
60-120 dollars,depending on overall condition and a good bore.
If we are talking about a stevens model 77 shotgun?Then these were made by stevens between 1955-1971.
I would start at the home page of savage firearms company,check customer service.Then you could look at E-bay and see if any have been reprinted.
These range in price from 60-140 dollars for a gun with between 60%-95% original finish remaining and a good bore.