In the US, perhaps we could stop the obscene subsidies for petroleum, corn, and meat, and subsidize more sustainable, nutritious and humane crops and farming practices.
If those existed and were cheaper, that would be done
If what existed? sustainable, nutritious and humane crops and farming practices? they do exist.
The person you're responding to said "existed and were cheaper," but you seem to have ignored the second conjunct of their claim in your response.
To be fair, that poster injected “and were cheaper” in response to a suggestion that subsidies should be moved away from substitutes and toward these practices, which probably wasn’t done in bad faith, but doesn’t exactly rebut the suggestion that subsidies would need to change to make this economically sustainable.
That presumes that those subsidies are for solely practical reasons, when in reality they're at least partially a political tool.
Of course they're not cheaper - they're not subsidized.