This should be a Savage 18-D.
http://www.histandard.info/PDF/Sears%20Shotguns.pdf
Its an H&R Model 120
$80-$100.
Stevens
A sidelock shotgun is exactly as it sounds. The locks are on the side of the stock instead of inside the action. A box lock has the hammer, sears, springs etc inside the action itself, side locks are primarily separate. They are attached to the action on the back and sides of it in the wood and the hammer, sears springs etc are contained therein. They can be detached without removing the action from the stock.
$65
Yo may not be able to- there was a safety recall of about 7 of the different 12 g bolt action shotguns. Sears is trading the bolts for a $50 gift card. Sear for Sears Shotgun Recall.
A bolt action Sears Roebuck shotgun would probably sell for $75 to $125 retail.
$75-$125, depending on condition.
Sears Roebuck co.
The JC Higgins 583.16 is a bolt-action 12ga shotgun made for Sears by High Standard in 1948/1949.
Marlin Model 59, 1959-1961