> Land in these places can be something like $500/acre. That's not zero
...and thus economically scarce...
> but compared to the land prices people are more familiar with, it's as close as makes no difference in practice.
It's very cheap. But very cheap things are still scarce. Something that isn't scarce has no price and everyone (even the poorest of the poor) who wants any quantity of it will have as much as they want without sacrificing anything.
Land in the places you describe is cheap. The price may even seem negligible to people in the upper middle class in the developed world. It's very much still scarce.
The difference between scarce and not scarce is not a matter of price, it's a fundamental difference of kind.
