Messing with the GPS signal around the area you need to protect is probably the most effective cheapest way of of defending an area ( no good near airports though )
Make more seance for a wide blanket ban near any airfield without prior permission. ( 10 mile min )
I dont thing jamming them is feasible, and like the other poster said, most would just carry on to target. You have to mess with the GPS. and its not hard to do, i think Iran did this to nick that USA drone a few years ago.