BOE Won't Fund Graduations So Principals Extort Money from Students? What's wrong with this picture?

Public school graduation is free in Maryland.  There is no legal charge to attend your own graduation from a Montgomery County Public High School.

The Board of Education got their budget request fully funded by the County Council this year!  How is it that graduation is not included in fully funding the public school budget? 

...Most Montgomery County high schools hold commencement at the Daughters of the American Revolution’s Constitution Hall in Washington, D.C., which costs more than what’s allotted by the school system, forcing the schools to charge students a fee to graduate...

 http://www.gazette.net/article/20140513/NEWS/140519867/-1/arena-at-shady-grove-metro-station-poised-to-advance&template=gazette