I dunno, seems to me that they're slow enough and fly low enough you could shoot them down with 50 cal ammo. The hard part is aiming and hitting them. But seems to me that someone could make a radar assisted point defense system that automatically aimed and fired a 50 cal gun, like automatic skeet shooting. Such a system would have limited range and could not hit very fast moving or high altitude targets, but would be cheap enough to deal with the cheap slow drones.