you may find some info at the savage arms website.This was the maker of your shotgun,savage/stevens.
Try e-gunparts.com
It's a Stevens 620.
If it is a stock gun it probably has a open cylinder unless someone has added a choke.
Assuming 12ga, $150-$250. sales@countrygunsmith.net
what is the value of a Ithaca 12 ga shotgun
Try e-gunparts.com
Stevens 520A
Mossberg
Turn of the century, inexpensive arm.
100-300
There's one for sale here in Canada -> STEVENS 311 12GA X 2-3/4" 2 BARREL FITTED SET, 20" IC/CYL, NRA GOOD $289 CDN