Your references are really fucking old.The interstate has always been paid for by each state. It's why when you have new roads in Idaho but get potholes in Montana. Or you drive on smooth roads in Texas but Louisiana his nothing but old, rundown concrete highways with bumps every 20 ft the entire length of the state.
Most of it was paid for the federal government.
The final estimate of the cost of the Interstate System was issued in 1991. It estimated that the total cost would be $128.9 billion, with a Federal share of $114.3 billion. This estimate covered only the mileage (42,795 miles) built under the Interstate Construction Program. It excluded turnpikes incorporated into the Interstate System within the mileage limitation and the mileage added as a logical addition or connection outside the limitation but financed without Interstate Construction funds.
In all, Federal-aid legislation authorized a total of $119 billion to pay the Federal share of the cost of Interstate construction. (Interstate Construction funds were authorized through Fiscal Year 1996.)
Interstate Frequently Asked Questions - 50th Anniversary - Interstate System - HiYou ghway History - Federal Highway Administration
Maybe you can find something that deals with 2017-2018 timeframe.
BTW, money means dick if you don't spend it properly. That's why all of the states get varied results.