The enemy gets a say in your plans, and is much more likely to have low cost weapons available then high cost ones.
The interceptor for a SHAHED is a quadcopter which doesn't need to fly as far or carry as much payload. Anyone can build this.
The interceptor for an Iskander ballistic missile is a Patriot interceptor: literally nothing else can successfully stop it reliably. Only the US can build this.
If your attacking systems are cheap, then the enemy can field just as many: Russia has a lot of drones in Ukraine now too, they were just playing catch up.
"The next war" won't have surprise drones as a problem, it'll have highly developed and optimized drone and counter drone systems.