Does your Savage 720 have the "Humpback" like the Browning Auto 5?
I believe that link you posted is listing that particular model on the high-end.
If it's the model that I'm thinking about they usually sell from 350 & up. Is there anyone local you can check the value of the gun with? I would hate to steer you wrong. The authentic Savage 720's WWII Trench Warfare shotguns with the US stamp on the side of the receiver have been sold to collectors for quite a bit of money. But of course if yours is a WWII model that saw action you would have to authenticate the gun.
I would keep it, but that's just me.
I'm a 12 ga. nut.
best of luck Bro.