If you're getting the phone at a subsidized price with a two year contract it will be $199.99 (plus tax). If you'll be getting it with the AT&T Next Installment Plan (depending on your area's taxes) you'll just be paying for the tax up front, and then $32.50 monthly for 20 months.
If you don't want to be tied to any type of contract (two year or installments) and would like to go month to month, the phone can be bought at retail price for $649.99 (plus tax).
Hope this helps!
*I am an AT&T employee and the postings on this site are my own and don't necessarily represent AT&T's position, strategies or opinions.