Surprisingly cheap. There's recently been a scandal unfolding in Norway where the parliament has been building a 250 meter long tunnel into its parking garage.

Surprisingly cheap. There's recently been a scandal unfolding in Norway where the parliament has been building a 250 meter long tunnel into its parking garage. Almost exactly 1/100th the length of the Lærdal Tunnel. So far this project has cost 2.3 billion NOK, or 1.3 billion more than the Lærdal Tunnel. That comes out to 1180 million USD per km. (To be fair, included in that price is also the renovation of a building external to the parliament).