The best place to start is with "The Blue Book of Gun Values". In your case, Savage shotguns are, for the most part, shooters - not collectibles. With "a few rust spots on the barrels" it's a $75.00 gun, give or take. Clean it up as good as you can, and keep it for a shooter. 000 or 0000 steel wool and oil, used carefully, will remove the rust - then you could touch it up with cold blueing.