As to killing them, you only need guided munitions with targeting capabilities. That or kinetic weapons, just ram them with something that doesn't even have explosives but sufficient velocity (actually similar but much cheaper version of ICBM intercept kill glide vehicles as you don't need to maneuver as fast or much).

The real cost is in getting things up that high as you usually have to burn quite a bit of fuel and there's the logistics of it. Ideally you'd engineer some sort of fast military orbiter with a grabbing arm and grab and chuck those things with force back into the atmosphere or just straight up crush them in space but that's a little sci-fi though it would be cheap for dealing with the potential of hundreds of these things. That or a low orbit fighter. But I could see an uncrewed re-usable hardened vehicle that just goes around ramming these things one by one and damaging or destroying them. Satellites are built to be light not to survive any kinds of impacts so something with a toughened hull should be able to take out quite a few just by hitting them at speed before firing thrusters again and moving onto the next one.