> the cost of interceptors is greatly more expensive than the cost of building the conventional missiles

And the same thing is true with this comparison. The cost comparison is not interceptor vs conventional missile.

It's interceptor vs conventional missile + the damage the missile would have done.

Yes, you don't want to use Patriots to intercept Shaheds but that's an argument for using the right tool for the job. It's not an argument that the economics of interception are completely broken.

Ukraine has interceptors that are cheaper than Shaheds.