There are missiles between the Stinger and the Patriot. The current stock of US radar guided missiles cost anything between 150k to half a million per round. Sure, probably not cheap enough yet, but getting there. And really this all comes down to range/capability. The current stock of missiles are designed to shoot down other missiles or aircraft, meaning they have to be really high-performance. For example, the AMRAAM has to fly out maybe 20-30 miles and then still have enough energy to chase down a maneuvering plane.
When you're dealing with a swarm of "cheap" drones, you won't need all that performance. It's cheap, so it probably wont be able to pull off those high G maneuvers fighter jets try. If it has a small engine (thus small IR), then it probably can't go very fast either. And it's range of its weapons is probably small too. So now you can build a missile with semi-active radar (like the Sea Sparrow), give it 10 miles (or even less). It probably doesn't even have to be supersonic (even cheaper!). So now may have a missile that's as cheap, or cheaper than most drones you're trying to shoot down.
Or, we might just see the return of large caliber AAA. Computer guided 88s. Yum.