The US Navy is largely responsible for long-range ballistic missile defense, since you have to cross an ocean to hit the US. They also have among the most sophisticated missiles for that purpose, capable of killing an ICBM at apogee. The inventory of these missiles is much larger, every destroyer carries them, and recent variants are often considered the most competent of the various ABM platforms out there.

These cost ~$30M. They are in the process of scaling up production to a few hundred per year, with some help from the Japanese. Unit costs are coming down. These same missiles are also being deployed for land-based ballistic missile defense, despite their naval origin.

In the long-term you are seeing a convergence of the missile platforms as more capabilities are compressed into fewer missile designs. The US is pretty clearly evolving their systems to more of a “missile truck” architecture that is optimizing for the number of targets they can kill simultaneously at the maximum ranges that make engineering sense. Many aspects of new platforms like the B-21 all point in that direction.

A historical limitation is that the rocket motors used by most air defense missiles really weren’t adequate for ballistic missile intercept purposes. The US has invested a lot in closing that gap.