Drones work now because they are $1000 (random number in the right range), while a patriot missile is $4 billion dollars each. Sure you could shoot a drone down with one, but if you do the enemy will just send more and bankrupt you.

I agree with the point but these numbers are some orders of magnitude off. A patriot missile is typically 4 million dollars (so not billion). Drones vary widely depending on the type. Man-portable scouting drones can go as low as a few hundred dollars. I don’t think a patriot missile would ever target something that small flying that low though. The Iranian Shahed is estimated to cost around $30-50k. Russia produces its own upgraded version (better navigation systems, bigger warheads, etc.) that costs around $80k.

Even then, you can make 50 drones for the cost of a single patriot. The economics are not favourable.