You want the really economical option? Just wait till night and set a small building near the horde on fire. You can either get the rush going using an air horn from hiding in the building, or just move down the street a ways and wait for it to start collapsing.
The noise of a burning/collapsing building is sufficient to draw in all Z’s from a several block radius, and they have absolutely no survival instincts regarding fire, so the vast majority of them will shuffle right into the inferno and be neatly incinerated.