Saying non credible af here, but in theory one could add a upwards facing shotgun shells on top of the helmet, triggered by a Camera/proximity sensor if it detects a drone/falling grande.
Maybe add a gyroscope to check if the helmet is actually facing upwards before triggering.
All in all unit cost could be below 250$
Drone dropped munitions rarely land directly on a soldiers head; rather they land nearby and injure surrounding soldiers with the blast/fragmentation. Without some sort of active aim, this thing will almost never hit, if it even triggers.
Let's kick it up a notch and get Raytheon working on a helmet-mounted Phalanx that fires .22LR. The old farts at the trap & skeet range are gonna be in for a surprise when I show up with that bad boy.