[amenhotep]

Patriots aren't the answer to Shaheds, but that's the wrong way to look at it. You don't compare the price of an APS charge with the price of an RPG. You don't spec your soldiers' ballistic plates by aiming to bring their cost down below the cost of the bullet you hope it'll stop. The plate is replaceable, the soldier's heart isn't, you sacrifice the thing you're happy to lose to save the thing you want to keep.

They're not happy they shot down $50k of drone, they're happy they shot down 50 kg of explosives that was going to strike a power station, it's not a hard trade to make.

[PeterisP]

A key difference from your examples is that the enemy doesn't have the capability to simply (and risk-free) send an arbitrary number of bullets at your soldiers' hearts or RPG rounds at your vehicles; the major "cost of delivery" is not the bullet/RPG but the trooper (and his risk) bringing the gun to get a chance to make a targeted shot with the bullet/RPG.

If bullets could leave the factory and magically fly straight at your soldiers, expensive single-use ballistic plates would not be a practical solution - you'd simply run out of them as you can't possibly produce as many of them as the enemy can make bullets.