Control systems are one per penetrator, aren't they? Same with nukes, if we're talking about them.
I'd say that it's exactly the fuel, the engine, and the whole chassis of an anti-ballistic missile what's so expensive. An ABM has very little time to do its job. It has to launch instantly, and accelerates at 100g or so, and then must also maneuver at this circumstances. It should also pack enough punch to destroy a warhead which is a relatively small metal needle, built to withstand the mechanical and thermal loads of an orbital reentry.
As a contrast, an ICBM can start with much more soft acceleration, can spend 10-20 seconds preparing for launch without loss of efficiency, and does not have to maneuver much during ascent and the orbital part.
No, penetration aids don't need any control system, they're literally just dumb pieces of metal. Of course they won't explode or be accurate at all, but that's irrelevant to soaking up interceptors which need to be a launched well before impact.
It's literally sending up some of the most sophisticated vehicles ever made by mankind to defeat mostly chunks of metal. Hence why even the US can't afford it in any meaningful quantities.
Everything on an interceptor is much more expensive because of the much higher performance requirements. But the fuel and structure will still be a lot cheaper compared to the rest of system.
Satellites in LEO and MEO can be destroyed with reasonably affordable conventional missiles nowadays, and it's impossible to hide or maneuver satellites in the few minutes it takes a missile to get up, so it doesn't really make sense to expect that any such system will survive long enough to do anything in a hot war scenario.
Hence why nobody really wants to weaponize space, spending money on military systems that have no survivability isn't very attractive.
I'd say that it's exactly the fuel, the engine, and the whole chassis of an anti-ballistic missile what's so expensive. An ABM has very little time to do its job. It has to launch instantly, and accelerates at 100g or so, and then must also maneuver at this circumstances. It should also pack enough punch to destroy a warhead which is a relatively small metal needle, built to withstand the mechanical and thermal loads of an orbital reentry.
As a contrast, an ICBM can start with much more soft acceleration, can spend 10-20 seconds preparing for launch without loss of efficiency, and does not have to maneuver much during ascent and the orbital part.