It's also pretty clear that some sort of resource footprint is more interesting than apparent living density. Just food requires more than a few hundred square feet per person and we consume a lot more than food.
You'll have to qualify that statement a little. Here is 5 acres of land in Texas for $1500 [1], found it in about 60 seconds.
[1] https://www.zillow.com/homes/for_sale/TX/land_type/209109538...
If you want to do brass tacks or whatever, buy it and scrape out a living to prove that cheap scrub desert makes a point about land being available.
Obviously water and other resources are going to be an issue, but as a labour multiplier, AI and robotics have huge potential.
Then that land (if not already privately owned and actually available for homesteading) will be homesteaded, privatized, enter the land market, and not be rent-free land that is available. Just like the land that was attractive for homesteading in the past has been. Sure, its a one-time land-rush just like the initial homestead act, but after that the same forces of centralization of property that always work in a capitalist economy will work on it.