I must get around to watching this video. I will say that I take exception to the thumbnail though: The Perth Metronet project finished up earlier this year, it costing $12.4 billion to roll out 72km of track.
On the surface, that comes out at about $172 million per kilometre. But, that is only part of the story. That money also paid for the construction/renovation of 18-23 stations, 8km of tunnels under the river for the new airport line, elevation of 5.5 km of track, removal of several level crossings, and a whole program to locally manufacture trains.
Just reducing the project to 'dollars per kilometre' would be super inaccurate for the overall result. But even then, that would be less than a quarter the implied cost of building a rail line in Australia from that thumbnail.