While exact evidence is hard to come by, I have noticed from casual observation that the price of airplane development programs seems to be trending downward even as the complexity of modern airplanes goes upwards. Here are some ball-park numbers that I submit as commonly accepted figures for some recent programs:

Boeing 777 - $15 billion (1995 dollars)
Airbus A380 - $15 billion (2005 dollars)
Boeing 787 - $8 billion (2005 dollars)
Airbus A350 - $10 billion (2006 dollars)

I expect that the A380 and 787 have both added a few billion dollars each due to delays, but I don't think the trend is too horribly disrupted. Adjust for inflation and the Boeing 777 cost about 25% more to develop than the A380; an aircraft almost twice as big. The Boeing 787 and Airbus A350 XWB programs will cost approximately half of what Boeing invested in the 777 for a like-sized airplane using more complex materials, aerodynamics, systems, and software.

The Triple-7 was notable for its heavy use of computer-aided design and Boeing had to invest significantly with IBM and CATIA to get the software they needed. As a result of the 777 breaking through the digital barrier, could it mark the "peak" of investment costs for a civilian airliner?

Thanks to virtual prototyping I imagine that the design stage costs a good bit less money now when you factor in the savings in materials and labor hours. You can have disparate groups quickly exchange information electronically without needing to fly people or product between them. You can also identify potential fitting issues before you actually start cutting parts.

First you have to have accurate estimates of the cost of the aircraft and I think your numbers are way off. That does not mean I know the actual costs and it is a liars poker game of the actual costs. So much goes into the real total costs that may or not be included in the costs reported to the press, such as facilities costs, R&D used in the new airplane that happened before the formal go ahead, overhead folks charged to multiple programs working full time during development, how much of your supplier costs are included, etc. If the 787 costs actually included major supplier sub assembly costs are, the the 787 costs would go up dramatically by several billion dollars. I know for a fact that the 777 cost more than the value given if you total ALL costs. I see no reason for the development costs to be down dramatically for new aircraft. I have heard that the computer aided design is supposed to save money, it does in areas and in other increases costs. With an airplane like 787 or A350 and the substantial increases in new technology I see no way the development costs go down. A real good rule of thumb for total cost is to compare the time between program go ahead and first production delivery, airplane to airplane. This calendar length is probably as accurate as any for comparisons from program to program. The quicker the actual schedule the lower the cost.