As an AT&T customer, how much will I have to pay for the iPhone?

I have heard some weird stuff about certain people having to pay more for the iPhone, and I was wondering if I am eligible. I have a phone (not iPhone) and I am almost half-way through my 2-year contract. My bill is lower than $99 (on one website it said something about the pricing of a bill affecting the cost). However, I have had to use my insurance to replace my phone twice, thus automatically cancelling my insurance policy (a website also said something about phone replacements adding to the cost of an iPhone). So, how much do you think I would have to pay?