The development cost of the Sukhoi PAK FA is around $8 billion. That of the Lockheed Martin F-35 Lightning II is estimated at $1.5 trillion right now (and may climb to $2.5 trillion in the future). And it seems that PAK FA is superior when compared to the F-35. So my question is, when the Russians can produce stealth fighters at one-hundredth of the cost when compared to the Americans, what prevented the NATO from purchasing the PAK FA, rather than wasting trillions of USD in to the F-35 program?