From the perspective of absolute cost, those things are absolutely cheaper. It's cheaper to build things closer together, period, because then you need less stuff. It's cheaper to build denser housing because it's less housing, and less land.
The reason this doesn't pan out is because cities are subsidizing everything around them. We take tax dollars from denser areas, which are the only areas that are economically viable, and then we redistribute them to suburbs.
It's time for that meme to die, cities are not subsidizing everything around them.
Cities would die without those "areas around them", because those are the places where food is grown and stuff is made. Adjusting prices for food via taxation is something the government does all the time, but if it didn't food prices would just go up, and cities would pay the same amount, just via a different path.
You might need less "stuff" to build things denser, but we've long passed the time when the main cost is "stuff". Labor is what matters, and building in a city takes much more labor.
In the real world non-cities are cheaper in every way, and that includes roads and utilities - and this despite needing more road and pipes.
The reason this doesn't pan out is because cities are subsidizing everything around them. We take tax dollars from denser areas, which are the only areas that are economically viable, and then we redistribute them to suburbs.