Hummm, 3 to 4 billion for 2400 km of new rail? The USA based DM&E has been trying for about 8 years now to upgrade a couple hundred miles of its track and put in a couple hundred more miles of new track - its billed as the largest new rail construction project in the USA since WWII (?) - and they are getting blocked at every turn. Total cost estimated is over 6 billion for well under 1000 miles (1600 km) of track. The Saudis will have to import the steel rail, wood ties - or set up a factory locally to make concrete ties, obtain large amounts of rock ballast, new locomotive, freight cars, passenger cars, build marshalling yards, stations, etc....
My guess is more like 30 to 40 billion minimum?
For more info on the efforts for DM&E to expand go to:
http://www.dmerail.com/PRB%20Project.html
Also Google DM&E Project to find out the opponents side of the story.
Major rail upgrades and expansion in the USA will take a LONG time if the DM&E project is any indication. From regulatory roadblocks, local NIMBY efforts, financial constraints, etc....
I tried to convince DM&E to go electric traction engines with overhead catanary power and they agreed it would be cheaper to operate that way, but they said they would not do it because it "would be more difficult to interface with the other non-electrified rail lines"
You have a long hard uphill battle for electrification of rail service in the USA - Until the price of diesel fuel goes through the roof - And it will be a bit too late by then?

Jon Kutz
Tinkerer and Dreamer