For our dog. She paid $25 at a yard sale. I hooked it up when I got home from work. The dog wasn't too sure about it at first. We had her in her harness and belted to the trailer so she wouldn't leap out.
I took her out on the street and kept an eye on her with my mirror. Her nervousness seemed to dissolve and the tail started wagging and she had that happy dog tongue hanging out and air sniffing thing that dogs do.
Only went for about a half mile total. Tomorrow we'll try the dog park. 2.7 miles one way. I sure can feel that thing behind me.