How much would an IPhone 4 to 4s upgrade cost?

So I have an iPhone4 with 8gb and I want to upgrade to the iPhone 4S (NOT the 5) with 32 gb. I've had my iPhone for a little more than year now and i was wondering about how much it would cost to upgrade? Also, how much would it cost just to upgrade from my 4 to a 4 with 32Gb?

11d7 dollars and yes I do mean 11d7

Lol
why would you do that
what's the difference between the two?

The iphone 4s is only available with 16gb, the other models have all been discontinued

if you are currently under contract, you have to pay FULL price for the replacement, if your contract has expired, you can pay the upgrade price.

It depends on how much the seller is willing to offer, if you are buying it second hand unlocked. Otherwise you can only get an 8 GB iPhone 4 (Apple is no longer selling this in other sizes, however it is $0 on contract). The iPhone 4s is 16 GB only and costs $100. But why not get the iPhone 5? It's better, has LTE (required at the moment for Cellular FaceTime on AT&T btw), bigger screen… It costs $300 btw.

After you upgrade you may need to extend your contract with AT&T or Verizon, but it is possible they will unlock your iPhone 4 at which point you can sell it on eBay or some place. Short of that I don't think you get any discounts for upgrading.

By the way, going from a 4 to a 4 with 32 GB wouldn't be worth the trouble anyway. If you need the space, delete some old apps and movies and copy old photos to your computer.