It might be tens of dollars rather than hundreds, that information is harder to come by, but it's not going to be cents. It's a lot of area of material, even if it's cheap material, and hydrogen isn't free either (helium is much much more yet). Plus, the drone costs what the drone costs.

Shooting from ground level probably isn't going to be the solution, because a balloon can fly higher than any heavier-than-air craft. Maybe bigger AA guns could be developed, but it's going to get less mobile, and eventually there's a fundamental limit to muzzle velocity set by the speed of sound in whatever detonation. Plus, if you're using large specialty rounds and a lot of them per hit we're right back to cost.

but the collateral damage from debris could be significant.

How so? There's a lot of empty farmland in the area, and it's wartime. It seems like unless the Ukrainians (or Russians; this will be copied) can still steer and reliably detonate the drone it's no longer an effective weapon.