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Just here to casually remind people that this naval anti-missile system called ‘goalkeeper’ exists.
And while it’d be very expensive to buy even just a few to use in major population centres, Ukraine effectively has a blank cheque from the entire planet to make sure that Russia stays behind its borders. 
But rockets are probably a better option in general. It means militaries who support Ukraine can use this opportunity to donate their ageing stock and replenish with brand-new munitions.
Russia makes the bet that Iran can produce drones faster than NATO can produce anti-air missiles. >

Honestly I think they’ll be able to do it cheaper with high volume computer assisted machine gun fire or computer guided anti drone electronic warfare weapons. 
Missiles are expensive but a tracked weapon that either doesn’t need reloading or costs a fraction of a missile is coming. >

cheapest is to kill the source, just need some long range, accurate missiles >

And most effective - I’d go for this option