I did a kicker several years ago with 2 legs that has worked for years, and was fairly cheap. Last year I moved him to another area, and tied his feet together, and hung him upside down, and he works even better.
Basically I just took 2 pieces of square metal rod, and cut them so that they were about the same length as the bones in a leg. I hinged them at the knee, and added a pivot at the hip, leaving rod extending above the hip.
I took a power window motor from a ford truck, and attached a offset bearing to the cable winder in the motor. I then mounted the motor so that as it turns it will push the upper leg bone rod as the bearing goes by.
It creates a kick that looks pretty good, and the best part is it has lasted year after year.