They'll probably have to study that, too. It depends a lot on the ridership levels, which are usually highly inflated to justify the project.
The LA MTA budget was $2.8 billion, and either had about a million passenger trips or cost $6000 per passenger, depending on the source. The MTA serves a lot of short-distance commuters as well as light rail.
The annual subsidies for the MTA are enough to build 68 miles times one lane at the price of the most expensive CA freeway (Century freeway, I-105). Obviously, one lane of freeway is used by many more than 1 million cars per month (let alone per year).