The cost of an adversary’s drone or other weapon is irrelevant. What matters is the damage any particular drone/weapon can do. If a cheap weapon is on track to cause $1 million worth of damage/loss, while an expensive weapon will cause only $1,000 of damage, take down the cheap weapon. What you are purchasing through the use of a defensive weapon is avoiding harm — use the defensive weapon in a way that maximizes the avoidance of harm/damage — Not based on the perceived cost of the target offensive weapon.
Whether Russia finds drones for free or pay high prices for them, the damage that they cause, and other opportunities for targets are the main considerations.