How much will it cost for Apple to replace the back panel only of my iPhone 4?

[JoshuaAlexander]

More specifically, the only thing that's wrong is the glass that covers the lens on the back. It's really scratched up and it's actually blurring my photos. I don't wanna sound like a whiner, but for someone who uses it as their primary camera, it's a bother.
I really don't want anybody else, but Apple fixing it either.