How much does an iPhone 6 cost with Sprint?

I've had my iPhone 4 for nearly 2 years. I know you can't upgrade until your contract ends, but the Sprint app says I'm eligible for an update. If I do the whole Sprint Leasing thing for 30 months how much would a 6 cost when you walk in the store minus the $35 for the activation? Like 16gb 64gb & 128gb.