The Galaxy S5 on AT&T would cost about $199.99 with a 2 year contract and if your wish to buy the off contact device, then it would cost you around $649.99. You can also with the AT&T Next plans on which the device would cost per month on AT&T Next 18 or $32.5/month with AT&T Next 12.
Also AT&T is offering smartwatches, the Gear 2 worth $299, and Gear 2 Neo worth $199 and also Gear Fit. And if you order Gear 2 and Gear 2 Neo along the Galaxy S5, you would be getting a discount of about $50. The or orders will behind tomorrow and the device would ship till April start. Just after the launch of the Galaxy S5, that is hopefully going to be on April 11.