How much does the model 9478 series Stevens single shot shotgun cost?

my be 1000000 $ or 5000000 $ or 10000000 $ Maybe, but you'll sell it a lot quicker if you only ask for what it's worth. $25 if only good as a parts gun, $75 if in nearly-new condition. If it's 100% like new, you might find someone willing to pay over $100.