How much would it cost to upgrade iPhone?

Okay so here's the deal… I've had my iPhone 4s for nearly 4-6 months but I really want to update to iPhone 5c. I'm obviously not ready to just upgrade for free so that's why I'm asking how much would it cost me? I'm on sprint by the way just in case any sprint users know. My sister had the iPhone four but she had hers for at least a year before she updated to the five c and it only costed her one hundred dollars and that's why I'm wondering what's the deal and I just need lots of details!

6 months in a contract with 18 months to go? Sorry, full price. Yes, I have Sprint. Best you can do is buy it, so say $400 ballpark, then sell your's to recoup some of the lost coin. That's about it. Get your sister to hustle a deal for you. Oh, and don't tear it up. Apple doesn't cover damage, and if it was warranty work, they'll just give you another 4s anyway. Best luck.

Whatever it costs to break your contract, plus any new contract

Yes you would pay full price, but i think sprint will give you like $100 dollars for your old iphone i think.
hope this helped