You're comparing what I assume is high end bus costs, as the prices I found for buses were much lower[1], to low end car costs and still ignoring the infrastructure costs. Yes buses and trains cost more per car but they use far less space during transit. Since our transit problems are due to peak throughout times we need far more infrastructure in terms of highways, bridges, etc if we plan around cars than if we plan around mass transit. As the poster you replied to said, if we can't get people to agree to fund mass transit due to the sticker shock when it's a much smaller price than building a highway or making tunnels, how are we going to get people to agree to fund all this extra infrastructure we'd need for everyone to have their own car for all transportation?
I'm hoping with automatic vehicles and tunneling this mass transit versus not mass transit dichotomy will just fade away. Automatic buses and cars could use the same tunnel. Just make sure the tunnel does not clog up by charging each vehicle by how much space it uses up. People are willing to pay for transportation, many just don't like paying for other peoples transportation.
With enough tunnels traffic congestion disappears. Unless for some reason you think people should just not be able to move around when they want to, this would be great.
[1]https://www.thoughtco.com/bus-cost-to-purchase-and-operate-2...