It depends. The US isn't the most or least expensive.

https://ipa.org.au/wp-content/uploads/2017/08/IPA-Report-Aus...

See page 5.

The US incarceration rate, though, is just nuts.

Not really. In 2014 the average in Europe was 103 euro per day, making that 37,595 euro per year per inmate. The variance is quite high since Sweden for example pays on average 226,665 euro per year, while Bulgaria pays 1,095 on average per year.

Interestingly, Norway which is famous for its rehabilitation focused prison system is cheaper than the one in Sweden, with around half the cost.

It’s far cheaper - because they mostly have an order of magnitude fewer prisoners per capita.

That's not how economy of scale works.

The price per prisoner isn't the relevant metric. Total price to society, from the cost of maintaining and manning prisons, from the cost of lost human connections with those imprisoned, and from lost productivity from those imprisoned, is a relevant metric. A prison system with a 36% 2-year recidivism rate (United States) is a failure when compared to a prison system with only 20% 2-year recidivism rate (Norway), no matter how cheaply it may be managed.

The goal of a functioning prison system is to manage itself out of existence.

Prison is not a free market and is not subject to market efficiencies. The purpose is to extract the maximum possible value from human suffering. They do this by charging them obscene prices for every basic necessity, double charging the government for their needs, renting them out as slave labor (mandatory work at wages of a couple of dollars per day), and then lobbying fiercely to keep their position. The private prisons want it to be more costly, beacuse they have monopoly contracts and guaranteed sales.

Prisoners, and taxpayers, do not benefit from economies of scale.

Capitalism here means getting the highest price per inmate, and getting the most inmates you can.

Efficiencies of scale are profits, not cost savings

I've no idea why you're getting downvoted.

Private prisons in the US negotiate agreements with the states with minimum occupancy clauses. [1]

Speaking of an amoral dereliction of duty of care.

[1] http://www.aublr.org/2017/11/private-prison-contracts-minimu...

Because what he describes is extortion not free market, there is a difference.

I think on a superficial level the whole system is not setup to deliver quality outcomes for anyone.