Looks like the tax payers got hosed during the G-8 demonstrations in Thurmont, Maryland, the town closest to Camp David. Demonstrators were bused in, and local police had to mobilize and bring in extra troops. Mayor Burns of Thurmont estimated the costs for his town at $20,000. This article from nearby Fredrick, MD has the crowd at 200 (and that probably includes the police!)
That works out to $100/protester out of the just the local PD for the two day summit. That doesn't include the millions that were no doubt allotted for the Government agencies who came from the Federal realm to deal with just this.
A note, this is up in "Liberal" Maryland that protesters had to be "bussed in". There is plenty of room for 200 tourists to pull in and eat or visit in Thurmont. So in Maryland, there appears to be little support for the hard left.