To me, that is one of the the big points about this order. It helps provide those economies of scale that the manufacturer needs to drop the price of each aircraft:
Once Seoul - as new buyer - formally notifies the Pentagon about its planned purchases, those jets will be added to the total number of expected purchases by the U.S. military and allies that is used by defense officials to estimate the cost of each airplane.According to the story the South Korean order could end up saving the US military about $2 billion. More foreign sales (outside the original allied partners) of the aircraft, the lower the cost of each for the US and it's partners. And, as the article points out, foreign buyers are showing increased confidence in the F-35 via their orders.
By 2019, the Pentagon projects the cost of each new F-35 fighter plane will be around $85 million, putting it on a par with the cost of current fighter planes, said Jim McAleese, a Virginia-based defense consultant.