Bullhorns are overrated
They cost too much and they don't work very well.
Most people ignore them, they don't last very long and they're undependable.
Anil Dash has discovered that having ten times as many Twitter followers generates approximately zero times as much value.
The goal shouldn't be to have a lot of people to yell at, the goal probably should be to have a lot of people who choose to listen. Don't need a bullhorn for that.