The Center for Economic and Policy Research put out a new report on the fiscal burden of the American prison system (pdf):
We calculate that a reduction by one-half in the incarceration rate of non-violent offenders would lower correctional expenditures by $16.9 billion per year and return the U.S. to about the same incarceration rate we had in 1993 (which was already high by historical standards). The large majority of these savings would accrue to financially squeezed state and local governments, amounting to about one-fourth of their annual corrections budgets. As a group, state governments could save $7.6 billion, while local governments could save $7.2 billion.
(Hat tip: Economix)