The lack of second chances we give in America to some of our most unfortunate means that even non-violent offenses can have lifelong consequences. It's shameful.
I think the cost has some influence over employers making a decision to hire an ex-con. If a store can hire someone for minimum wage without any conviction records, why would they hire someone with conviction records when they can't pay any lower than the minimum wage?
Even at the lowest level, not all employees are equally productive. And even at the lowest level, there's something to be said for "loyalty" - for the employee genuinely trying to act in the best interest of the company.
Money is just one way these sorts of behaviors can be incented.
I like to give the example of the choice of hiring a citizen vs. hiring a H1B worker.
Even if the company does pay them the same as a citizen, the employer has rather more leverage over the H1B, as if the H1B gets fired, they've got two weeks to find another employer that can sponsor their visa, or to get their shit together and get out of the country.
There's the positive side of that, too; If you take a person that has never been given a chance and give them a chance, well, there's a chance they will feel grateful, and attempt to return the favor... whereas if you hire someone who gets five or six phone calls from recruiters every day? You probably aren't going to get as much gratitude from that person.