I had never heard of this. How much? You know, friend....
These Air Force ‘Rods from God’ Could Hit with the Force of a Nuclear Weapon
These tungsten rods could hit a city with the explosive power of an intercontinental ballistic missile.
www.military.com
I think I ran the numbers once. Let's say "Small Nuclear Weapon". But in theory, very precise targeting.
Kinetic Bombardment is a really simple mechanism. All you have to do is bully something heavy and durable (like a meterorite) into the gravity well, and have some rudimentary way of inserting it into a decaying orbit. Physics does the rest.