It would be great to think that the cost really will continue to drop, but will LM really do it, especially if they are now having to absorb any increases? How many previous projects ever went down in price?
The project costs may increase as its basically R&D, but the manufacturing cost is determined by volume. And the number built will have a major effect on cost per unit.
The F-35 is not in production yet, so yes, cost will come down significantly when three or four times as many are build on the same line.
The low cost of the F-16 and other American aircraft (B737?) is not low due to brilliant design, its entirely down to mass production.