In your worldview: the government subsidizes rural life by... building roads? Making gas cheaper?

How does all the food grown in rural areas make it into cities? Not by teleportation; by being loaded into semis, driven on roads, using gas. There's a cost. When roads get worse, when gas is more expensive; food gets more expensive; and it gets more expensive for cities more than it gets more expensive for rural areas.

That's... subsidizing. For cities. We live in an interconnected economic system. The fact that cities make more tax revenue, then export some of that tax revenue to rural areas to support their public infrastructure, does not mean cities are subsidizing rural areas. It means that cities need rural areas to survive, or at the very least, to keep costs affordable.

> Food is an incredibly substitutable market, you'd expect the market to push prices down to a minimum.

This is largely the reason why we have subsidies for farming: we're not okay with substituting domestic agriculture for foreign imports, due to the risks involved. Consider the case of manufacturing, which is also a largely substitutable market.

In the late 20th and early 21st century, the USA hollowed out loads of our manufacturing hubs in pursuit of lower prices, and this worked as advertised; costs dropped! With circumstances changing and a desire to perform more domestic manufacturing, though, we've lost a lot of our options. The USA has lost a lot of manufacturing nous and industry momentum, meaning that there's a lot of upstart cost to get back into the game.

While subsidizing an industry may not be efficient from a global market perspective, it can be very sensible from a national policy perspective, since it means that you can build an experienced workforce and institutional knowledge within a given domain.

This isn't as clear cut as you are making it. A lot of infrastructure haa pushed the price of food down. As prices go down, so do margins. Making a living as a farm hand has better margins without the interstate highway system for example.

The supposed "subsidies" to rural areas are the cost of creating the low prices which cities also reap a lot of benefit from. You in fact could not easily substitute rural monoculture for something else. Not at today's prices.