If it's anything like the automotive industry, their customers already have a contract that specifies the price going down for the next decade. Customers know that you'll improve your process, get more efficient, develop a supply chain, learn to spot problems before they surface, automate repetitive actions, and train your technicians as the years go by.

The contracts specify prices and quantities years in advance - with later years at lower cost than the first years. I suspect that someone guessed years ago that while these titanium parts might need to be made with expensive machining initially, they could eventually be built using EDM, casting, or 3D-printing, and factored that into their budget at Boeing or their contract as a customer.