If you are still building your prison and you run out of money order your workers to cut down all the local trees and sell the lumber. Medium security prisoners are “just right”, if you plan on running a pretty standard prison. Of course, that means that having only high security prisoners should be the most profitable option, but if you do not run a tight ship, and you lack in actual security, then do not try your luck with high security prisoners. Depending on the Security level of your prisoners (low, medium, high) each prisoner will give you a specific amount of cash at midnight ($50, $100, $150).
Firstly, money is generated through your prisoner numbers. There are a few ways of approaching this problem.