We're not doing fine.
"New York’s Second Avenue Subway cost $2.6 billion per mile... The approximate range of underground rail construction costs in continental Europe and Japan is between $100 million per mile, at the lowest end, and $1 billion at the highest. Most subway lines cluster in the range of $200 million to $500 million per mile."
https://www.citylab.com/transportation/2018/01/why-its-so-ex...