How much will I have to pay for an iPhone 6?

My family has AT&T and I'm eligible for an upgrade. I want to get an iPhone 6 but IIm not sure how much it will cost monthly. Both of parents have unlimited talk and text and so do I. We also have a tablet. All four devices are on the 10 GB mobile share plan. How much will I have to pay monthly for the iPhone 6?

Added (1). The iPhone 6 will probably be on a two year contract.

Best would be to contact AT&T

Your ignorance amazes me, it doesn't matter what they say, they can always increase their rates.