Where do I go to get my cracked iPhone 4S fixed and how much does it cost?

Ok so recently my friend accidently dropped my iPhone 4S and the back cracked its pretty bad! It still works perfectly and luckily the front isn't cracked just the back so yeh. We're do I get my phone fixed? And how much is the cost of repairing it?
Soz for the bad spelling I'm typing this up on my iPad so ya.
And if I sell it parents ARNT going to buy me a new one ok I've already got 3ipod touches, 2ipod NanOes, 1ipad 2, 1 iPod shuffle and for Xmas I'm getting a MacBook Pro so I don't need anything! Else!

If you are paying for the apple care plus, a one time fee of $99 then you should be able to take it into an apple store and get it replaced/repaired for $50.