Even if we ignore externalities and pollution costs, just stop outright subsidizing animal meat production so much. The reason meat is so cheap is because our government puts a lot of effort and money into making it cheap.
I don't know why more people aren't trying to sell this to the "free market" crowd as government overreach. The reality right now is that plant-based protein is gaining popularity despite the market being artificially biased against it in terms of price. Animal meat should cost more than it does, not just in the sense of "you're not paying for the true environmental cost", but also in the sense of, "you're not paying the actual monetary cost it takes to produce this product."
The US government throws billions of dollars into subsidizing meat and dairy production every year. Plant-based protein's growth is restricted in part because our food prices and production aren't determined just by the free market. That's not necessarily bad, but if we're going to be messing with the market anyway we could choose to subsidize other things.
And we could obviously do more than just lowering subsidies, I'm not saying we should ignore externalities or that we should just completely abandon all subsidies entirely. But I am saying we shouldn't pretend that meat actually costs what we see in the store. Meat is cheap because (for various reasons) as a society we've all collectively decided to spend tax money so that we can pretend that it costs very little to produce.