Variant of a suggestion from Reddit: the original is to transfigure the Earth into gold for a nanosecond, along with a trail that reaches out to the Pioneer probes. The goal being to hit all horcruxes at once, and at the same time transfigure the death eaters and LV to kill them horcrux-less. This is supposed to 'work' because it's for a short amount of time.

Bearing in mind that the magic cost is dependant upon target size, I'd like to suggest another option: transfigure the cubic kilometre below them into a small diamond, or better yet, transfigure it into a slew of tiny bullets travelling at 0.1c and aimed everywhere except a cylinder centred on Harry. The target size (the bullets) is small, so this is feasible in a short time frame whilst causing mass disorientation as everyone suddenly is hit by 1g downwards acceleration and 0.1c bullets.

If I've misinterpreted the phrase target size, be aware that the opposite plan is also OP: simply transfigure the layer of dirt you're standing on (if that's what target means) into a 2km tall tower, then apparate.