Why spend hundreds of millions on prisons? Here is the answer. Modular, cheap and spartan.
They don't need toilets in their cells- a 10 litre pail does just fine- it could even have a lid!
Showers and toilet modules are also available, although I see no problem in outdoor facilities.
Ring the whole damned facility in four layers of barbed wire and you have a facility built in days rather than years.
Never mind the landscaping- the crims have plenty of time on their hands for barrowing gravel for paths and laying lawns- on what land isn't used for growing cabbages and potatoes.