How much is an 1803 commemorative nickel that's upside-down on the back with the front side upright when you do a coin turn?

Assuming you're referring to one of the newly issued nickels .... If you are flipping it top-to-bottom (as opposed to side-to-side), then you have a very rare rotated reverse error. If certified, these can sell for over $100 However AFAIK there are no reports of rotated die 2004 nickels. The best thing to do is to compare the turn with other coins from your pocket change. If your nickel does not have the same orientation as the others when flipped the same way, you've make quite a profit. If the coins are all the same orientation, you're five cents richer.