75-300 USD depending on conditon.
the savage Stevens no 311 was made between 1926-1945 with 145,500 units made.
Not much in the way of serial number data on Stevens guns. Check with the customer service staff at Savage Arms- Stevens has been part of the Savage brand for nearly 100 years. http://www.savagearms.com/customer-support/
50-300
I can say that the Stevens model 311 side by side shotgun was discontinued in 1989.I would go to the Savage arms web site,they may be able to help you find out when the manufacture of your shotgun was started.
I just paid $375 plus 71/2 % sales tax for one in NRA very good condition. It was probably never used; still had original Stevens sales tag on it.