[chrisco255]

Do you have a quote on someone building a tunnel of equivalent circumference for $10 million / mile? Or anything close to that? By all accounts everything I can find suggests closer to $100-300 million per tunnel mile.

One example I found was the English Channel Tunnel, which cost $21 billion for 32 miles of length. It's a two way tunnel, so at $21 billion / 32 miles / 2 bores (plus 1 utility bore)... $218 million per mile (avg), and I'm not adjusting for inflation (completed in 1994).

https://www.engineering.com/Library/ArticlesPage/tabid/85/Ar...

[bryanlarsen]

Here's an example at $20 million for 9 miles:

https://www.tunneltalk.com/Toronto-sewer-tunnel-Sep11-Straba...

This is a 12 foot diameter tunnel, exactly the same size as Elon's.