Apparently Phalanx CIWS ammo costs $15-30 per round (numbers all over the place depending on ammo type and age of information).

On the other hand engaging a target typically uses 100+ rounds or ~$1500-3000 per target.

Definitely cheaper than a good drone (~$5000-20000?), but maybe not far cheaper.

we're not at war tho, so you don't have economy of scale in place, those will benefit especially low tech ammunition - i.e. solid bullets as opposed to guided munition/drones - I expect the former to came down in price a fair bit once the big order gets put in, while drones chip production will always be tied to silicon yields economies and will benefit a little from scaling, but not as much.