Look at it this way. How much does it cost to maintain the OMNY and MetroCard systems, to maintain the turnstile infrastructure, and to maintain staff to prevent people from skipping payment?
From a quick search it seems the OMNY system cost $772 million to create and $15.5 million a year to maintain.
Stats say that 82% of those ticketed for fare evasion and 92% of those arrested were people of color. There's a social cost to that, but I couldn't begin putting a number to it.