Given advances in satellite navigation and terrain mapping, think about the implication of trying to counter drones that can hug a couple meters or even much less above ground level.
Or drones that can be pre-deployed to very precise positions as intelligent mines prior of enemy passing through.
Drones than can be used to harass, delay enemy advances to cover for a retreat.
Drones landing on top of hills/vantage points beforehand, using cameras to recon passage points while remaining low observable themselves, not needing food or water and not getting tired.
Cheap but fast drones carrying radar reflectors to make enemy waste expensive long range SAMs. While real jets hang behind waiting for opportunities to go for the kill.
I definitely think Smart mines will be the case in the near term.
Besides costs, there will also need to be more development in both sensor quality and machine recognition of targets.
The way I see it, versus my own scenario posited, the greatest advantage of a drone is ability to loiter and perform precision attacks.
I was told that one of the most popular Taliban harrassment methods were Grad rockets hooked up to crude timers. Just dropping it off near a FOB and concealing it.
Similarly those trucks could lay a drone field and retreating. Targets passing through could be recognized/prioritized by computer and man in the loop would accept/reject to launch attack.