To put this into perspective, China's high-speed rail project in Indonesia connecting Jakarta and Bandung (a distance of 143 km) at a speed of 350 km/h was completed in just four months at total cost of $7.3 billion.
This line has seen an impressive number of passengers, with approximately 2 million people utilizing the service.
I don't think the money is the problem. For one thing, it shouldn't cost $100 billion. The Kyushu bullet train was built in 2004 and cost $6 billion. It's 159 miles long. The SF to LA train would be around 390 miles long, and yet would cost over 15x that of an equivalent Japanese train.
The problem is the private companies contracted for this thing don't actually want to build trains, they want to make a profit. They make enough of a profit from scamming tax subsidies, so they never actually have to build the train.