It takes very large amounts of money, skill and time to develop and run an intelligence network capable of pulling something like this off.
As counter intuitive as it seems these organizations are extremely risk averse because to them risks means years of work down the drain, opportunities lost and often for good and quite likely dead assets and or agents.
A $200 or even a $2000 drone doesn’t minimizes these risks it introduces additional ones.
Killing someone in a hail of bullets is easy and reliable, using a toy with a small explosive attached to it isn’t.