How much does it cost to add a line on AT&T and get a iphone5s?

I'm getting a line added to an account for AT&T and I wanted to know how much it will cost to open a line with a iPhone 5s.

It should only be the cost that is listed for that phone for a new two-year contract.

Well, inking a new contract for the line the phone will be roughly $100 with about $39 activation fee and maybe a few bucks for the line depending on how it falls in your billing cycle--they'll prorate. The line amount you need to ask them. Depends on your current plan and each line of sharing actually gets a few bucks cheaper than the last one. Best luck.