The future is drones and so many in the air force know it. Not sure why they haven't bet fully on it. I guess there are no dog fighter drones yet but the first time a supermanuverable <10m drone destroys a 100m manned fighter well it is all over.
Modern fighter aircraft are expensive because they are relatively large and crammed with tones of expensive avionics and sensors. Increasingly, the quality of your sensors and your ability to evade detection are more and more important while maneuverability is less important because of said missiles. Better sensors are larger and require more power to operate necessitating a larger aircraft. Also, the number of Gs an aircraft can pull is limited by both human survivability and airframe strength. This means as the size of the aircraft increases the max number of Gs it can pull will decrease. Missiles can pull 50 Gs. Even if you remove the human, no aircraft large enough to carry the necessary sensors, fuel, and weapons to be combat effective will reach even 1/3 of that because it would rip the wings off.