And there is nearly no oversight on how much these private companies are allowed to charge those 150K people for something that is court mandated. These interlocks can exceed $100/month for some of the poorest people in society.

Unfortunately the US public has no interest in this issue. They have a dual morality where lawbreaking is wrong, but profiting off of criminals and the poor isn't. So mandatory prison labor, expensive monitoring, for-profit probation services, and for-profit jails are fine.

Literally if you don't pay or play, you go to jail. But it was a plea so you "volunteered" (to not go to jail).