Brian,
As others have pointed out, don't get too discouraged on this idea. It takes time and ultimately orders to make a 3rd Rail / GGD project happen. Some projects sit on the shelf for years before they become a reality. Scott is very much about building what his customers want to see built as long as he can make his bottom line work. I personally think this train would make an excellent set.
To make the project work, you must reach out to the 2 rail community as has been mentioned. 50% or more of 3rd Rail and GGD product is 2 rail these days. While some on this side of the forum may see a $250 aluminum passenger car as expensive, this is half the price of what is available for a two railer who can only get it in brass otherwise.
As to the details of the train, my numbers mentioned above are accurate for today's pricing and probably are good for the near future. The big component is finding someone who has the information on each of the cars in the business train, the floor plans and the window configurations among other critical details. As I recall, several of NS's cars came from Conrail's business train set and I am assuming some are former Norfolk and Western cars. If anyone has that information, the set may come together much easier. For example, does Sandy Creek still have the same configuration as it did when it ran on the 20th century limited? I know it has had several owners over time. If it does then the design work is mostly done outside of graphics. On top of that, if someone has the heritage of each of the cars, there is a chance that a limited number would be painted for the original road to offset the minimum car order of what is normally 2000 cars total. Single car purchases interest some, while others want complete sets.
I'd also consider marketing this to go with anyone who has a J-611 since it will soon be pulling these cars. The F9s need some research, but as I mentioned earlier, if there are enough orders to justify a modified tool for the F9 in addition to the F7, it can happen.
Keep up your efforts and don't get too discouraged. This is a good project idea and it just needs to get promoted in the right circles. Right now the pre-orders for both the Powhatan Arrow and the Cincinnatian are strong as prototypical five car sets because not everyone can run an 8-12 car set on their layout. This is a train that has run in shorter lengths and has been pulled by lots of different NS locomotives beyond the F9s. The generator car alone would be a very interesting piece for any modern passenger car collector.
Hang in there and keep lobbying!