"This report estimates that legalizing drugs would save roughly $41.3 billion per year in government expenditure on enforcement of prohibition. Of these savings, $25.7 billion would accrue to state and local governments, while $15.6 billion would accrue to the federal government. Approximately $8.7 billion of the savings would result from legalization of marijuana and $32.6 billion from legalization of other drugs.
"The report also estimates that drug legalization would yield tax revenue of $46.7 billion annually, assuming legal drugs were taxed at rates comparable to those on alcohol and tobacco. Approximately $8.7 billion of this revenue would result from legalization of marijuana and $38.0 billion from legalization of other drugs."
Miron, Jeffey A., and Waldock, Katherine, "The Budgetary Impact of Ending Drug Prohibition," The Cato Institute (Washington, DC: Cato Institute, 2010).