Something that was not really anticipated prior to the start of the Ukraine invasion was the extent to which relatively cheap one-way attack drones have overtaxed the ability to manufacture and supply the very expensive defensive missiles

Consider that the current Russian strikes against Ukraine consist of 90% plus low-cost drones with the remainder being a mix of ballistic missiles and high-end cruise and hypersonic missiles. The Ukrainian aggregate intercept rates are amazing averaging 92% or more.  This kind of hides a brutal fact though.  There are categories of missiles that the Ukrainians struggle to intercept, or they have the capability that the missile defense crews must make fast decisions on what to engage due to limited stockpiles of capable munitions.  Patriots can knock down ballistic missiles, but Ukraine does not have a lot of them and so they must reserve them to defend particularly valuable targets.

This disparity in air defense is what drives the Russian campaign.  They can send several hundred cheap drones to figure out which targets are weakly defended and then expend cruise or ballistic missiles to hit those targets.

This same issue has affected the US in the war against Iran.  High end interceptors are not only expensive, but the lead time to build them is also very long and the US does not build them very fast and lastly, it will be difficult to ramp up production in any kind of timely manner.  This is no longer World War II where weapons go from drawing board to battlefield in months, it now takes years and the US is not the industrial giant it was even 50 years ago.

It would appear that currently the advantage in this realm is in air defense if interceptors are available, but as soon as those are depleted it switches to the attacker.

Just look at the effectiveness of the Ukrainian counter campaign in Russia.  Russia is so huge that they have difficulty defending even the most critical targets and for political reasons they must defend sites that are not critical leaving them even more stretched.  The Russians are currently in the mode of defending everything and thus defending nothing.

The following tables show the cost of attack drones and interceptor missiles.

Cost-Effectiveness of Selected Russian Weapons 
WeaponCost per unit (USD)Hit percentageCost per target struck (USD)Payload (lbs)Cost per 1,000 lbs of payload (USD)
Shahed drone $35,000  10$353,535  110$3,213,958  
Kh-22 $1,000,000  95$1,057,082  2,200 $480,492  
S-300/S-400 $1,500,000  100$1,507,538  300$5,025,126  
Kh-59 $500,000  29$1,748,252  700$2,497,502  
Iskander-M $2,000,000  90$2,224,694  1,000 $2,224,694  
Iskander-K $1,000,000  36$2,747,253  1,000 $2,747,253  
Kalibr $1,000,000  20$4,926,108  1,000 $4,926,108  
Kh-47 Kinzhal $15,000,000  74$20,161,290  1,050 $19,201,229  
Tabel source: Neil Hollenbeck et al., Calculating the Cost-Effectiveness of Russia’s Drone Strikes, February 19, 2025, https://www.csis.org/analysis/calculating-cost-effectiveness-russias-drone-strikes.
Most common non-Russian or Chinese ADA systems and estimated cost based on OSINT
Next Generation Interceptor (NGI)$111,000,000.00
Ground Based Interceptor (GBI)$90,000,000.00
Standard Missile 3 (SM-3) Block IIA$27,915,625.00
Centurion (C-RAM) - Gun System$15,000,000.00
Terminal High Altitude Area Defense (THAAD)$12,600,000.00
Standard Missile 3 (SM-3) Block IB$10,500,000.00
Standard Missile 6 (SM-6)$9,574,400.00
Patriot PAC-3$3,729,769.00
Arrow 3$3,000,000.00
Meteor BVRAAM$2,398,000.00
Standard Missile 2 (SM-2) Block IV$2,100,000.00
Aster 30 (SAMP-T)$2,000,000.00
Evolved Sea Sparrow Missile (ESSM)$1,809,933.00
VAMPIRE Missile/MANPADS$1,400,000.00
Gepard Flakpanzer - Gun System$1,200,000.00
NASAM AIM-9X$1,181,018.00
NASAM AMRAAM 120$996,736.00
Rolling Airframe Missile (RAM)$917,984.00
BARAK-8$553,435.00
Mistral M3$545,600.00
Stinger Missile/MANPADS$480,000.00
IRIS-T$450,000.00
Aspide Mk1/Mk2$100,000.00
Tamir (Iron Dome)$60,000.00
Directed Energy (Iron Beam)$3.50
Source: Various industry websites and news media reports