Rich or poor doesn't play into it EM. It's another way to make jail a place where people don't want to be, while helping taxpayers defray the cost. Jail should be unpleasant as a deterrent not to come back. If they want cookies and humanity, they can have that by not victimizing others and staying out of jail.
But what if they are indigent? Do the incur a debt for their time in jail? ANd if they don't pay, do they go back to jail? Not gonna fly in court, would be my bet. Long time ago, back in law school days, I had to go to lovely Gadsden, AL to interview a guy who couldn't pay his fine so was incarcerated in the jail. Every day he was in jail, $10 was counted off his fine. Court overruled that as it punished the poor only and not the rich. Making them pay is a great idea in theory, but can't see it working.
In prison, most prisoners have jobs that pay pennies on the hour, jobs that would pay probably significantly more than minimum wage on the outside. By paying the inmates a pittance that they can use in the prison store, the state makes money, the prisoners get a little something and maybe learn a skill. But by definition, jail can be for only 2.5 years or less (at least here) so it doesn't work up here for that.