I'd imagine the cost of arrests and incarceration are sunk costs though.

It's not like we pay the police $2,000 for each arrest, or pay the prison $500/night per inmate.

Does anyone know if these numbers were taken by adding up the costs of running a prison and police department and dividing by the number of arrests and inmates?

If so, it's a little disingenuous to make this argument.

Also, these cases are not about a 1:1 relationship of harm to society vs. cost of justice. If you let the crimes go, you'll have more people doing it because "everybody does it".

60 days in jail does seem pretty excessive though. If imagine tons of young kids or people in a rush would make a silly mistake.