[Adverblessly]

> Any missile you use is way too expensive relative to the price of the drone.

My understanding is that you use a laser, though I don't see why even regular AA guns wouldn't work, especially if it is trying to crash on you, meaning it needs to get very close.

> Plus, even if you detect it, it's coming towards you at a speed of 100+ kmph with the intent to crash into you and detonate the payload.

That will at least help you distinguish it from a bird :) Plus, I suspect that in any military conflict, you'll be more than happy to eat the cost of frying a few birds if it means you stopped the enemy's drones.