This is the downside of being Apple -- just as they get prices and costs to where they want them, those same prices and costs tend to go up again. Foxconn's parent company Hon Hai has reported that it will raise its manufacturing prices in China, directly affecting Apple's and other companies' costs over there. The company is reportedly trying to push profits up for the last quarter of this year, and aims to raise sales by as much as 30% next year.
Of course, this probably isn't a surprise for Apple -- given how closely the company researches and follows component costs, this is likely something already baked in to their strategy (and even if it's not, $40 billion in cash tends to help out with unseen charges). But it's a clear reminder that costs aren't fixed for these devices at all -- just because Apple secures pricing on one processor or screen doesn't mean they'll have that same opportunity next year. It shows you a little bit of just how difficult it is to do what Apple has done, and coordinate all of these parts and companies to make a great product at a salable price.