I would gladly pay a large high-income tax to get an amazing transit system. Something like a 5% tax on income between 100 and 200k would probably do it.
What makes you believe so? The better coverage public system has, the less effective it is. At very low coverage, where you cover only a handful of popular routes, it is indeed much cheaper than private SOV transport. At the other extreme, where you have a regular bus coming every hour to every house in very sparsely populated area, it wil obviously be very expensive and inefficient. Thus, somewhere between these two extremes, there must be a break even point. Public transit can be definitely be cheaper and more effective, but it isn’t always automatically so.
Cost is not the whole story. Electric buses are starting to become a thing too.
Yes, if you arbitrarily exclude the labor, which is a big fraction of the total cost, and conveniently assume enough demand (capacity factor) to cover for higher vehicle costs and higher fuel costs, then yes, public transit will be cheaper. That's what I meant when I said that for highly popular routes it will be more cost-effective.
In real world scenario though this rarely works out for real systems out there. For example, I live in Seattle. The metro bus system is quite extensive and offers good coverage, by national standards. The bus fare here is $2.75 per ride. The farebox recovery is 27%. This means that to cover all operational costs of the bus, the fare would have to be $10.20. Suffice to say, it is much more expensive than total cost of owning and driving a car, as long as your trip is less than 20 miles. Bus trips this long are here absolutely miserable: 20 miles bus ride in practice means at least one transfer, and so instead of 20-30 minute drive, you're looking at 1:30h journey, assuming no traffic of course.
Obviously mass transit makes less sense without the masses, in cases like that there are many places that offer community bus services that operate more like taxis. You call and say you want a pick up and the bus will pickup and drop off anyone else along the way. Think uber pool but half a century older.
There are even private companies that run free shuttles just to get old ladies pumping their pensions into poker machines.
Let's say that the city got 10 times more buses i.e. 10,000 total. That's 100 people per bus, which should be adequate for everyone to use transit, even with the constraints of how bad the city design is (really wide roads, too many curves and deadends, spread out suburbia). Buses cost about half a million which is maybe 25x the cost of a car. So, the 10k buses would be equivalent to about 0.25 million cars in terms of capital cost. Which is a factor of 4 improvement on the number of cars in terms of capital cost.
But, reduced capital costs is evidently not what people in developed economies are actually necessarily after. Turns out, people are perfectly happy to spend extra resources to acquire exclusivity rights to a vehicle, because of flexibility it affords them. Having a private transport allows you to go where you want, when you want, and in almost all circumstances do it much faster than via a bus. The opportunity cost of time spent walking to bus station, waiting for a bus, and then taking longer to travel is for many people very significant, thus they pay for private transportation to recover some of that time.