Cato's Walter Olson observes:

Federal grants drive police militarization. In 2012, as I was able to establish in moments through an online search, St. Louis County (of which Ferguson is a part) got a Bearcat armored vehicle and other goodies this way. The practice can serve to dispose of military surplus (though I'm told the Bearcat is not military surplus, but typically purchased new) and it sometimes wins the gratitude of local governments, even if they are too strapped for cash to afford more ordinary civic supplies (and even if they are soon destined to be surprised by the high cost of maintaining gear intended for armed combat).

As to the costs, some of those are visible in Ferguson, Mo.