You’d need a pretty big gun to reach that high. Something like a ZSU or Vulcan wouldn’t do. A 76mm gun might do it, but I don’t think there are any modern SPAAGs with guns that big out there. The Italians had one called OTO, but I don’t think they ever produced it.
But when we’re talking about developing a new, armored self-propelled AA gun that can engage high-altitude targets with low radar and IR signatures, I don’t think we’re talking about “cheap” anymore.
It’d probably be cheaper to arm your own drones with Stingers and have them run combat air patrol.
It carries 9M38M1 missiles that have a ceiling of 46,000 feet.
There's also the 2k22 Tunguskas, which currently can fire its missiles and hit up to 20,000 and the current upgrade under development will hit to 25k or 30k.
On the offense side, drone development is drilling down to the platoon and squad level. Deployed now is a drone recon system in a backpack for platoon level recon and fire spotting. At the squad level, field testing is going on with drones smaller than a hummingbird for CQB and to see around that next corner.
Drone swarm devices are in advanced development. These can be autonomous or man-in-the-loop. Think of a swarm of inexpensive and expendable drones thats that are are a mix of anti-armor, anti-personnel, radar homing, electronic jamming, etc. and are delivered by cruise missile or aircraft. For these, think of a clusters bomb dispenser that releases a mass of small drones with several hours of loitering time.