Unfortunately, some people on the conservative side of the political aisle have jumped on the "let-em-out" bandwagon because they see that as a way to reduce government budgets.  Looking at costs to government alone, however, is not the correct way to measure costs of alternative courses of action to society as a whole.  When government fails in its fundamental obligation to protect people from crime, it imposes costs on the victims, a kind of "crime tax" that falls heavily, partly at random, but disproportionately on people of modest means.  Quantifying the cost of crime to victims is a tricky business in many ways, and one of the ways is that much of the cost is hidden.  Science Daily has this article on a hidden cost that has been overlooked to this point:

In a recent paper published in the Journal of Development Economics, researchers Professor Marco Manacorda (Queen Mary University of London) and Dr Martin Foureaux Koppensteiner (University of Leicester) focused on evidence from the exposure of day-to-day violence in Brazil by analysing the birth outcomes of children whose mothers were exposed to local violence, as measured by homicide rates in small Brazilian municipalities and the neighbourhoods of the city of Fortaleza.

The team estimated the effect of violence on birth outcomes by comparing mothers who were exposed to a homicide during pregnancy to otherwise similar mothers residing in the same area, who happened not to be exposed to homicides.

The study found that birthweight falls significantly among newborns exposed to a homicide during pregnancy and the number of children classified as being low birthweight increases -- and that the effects are concentrated on the first trimester of pregnancy, which is consistent with claims that stress-induced events matter most when occurring early in pregnancy.