I built one using the drag axle from a small foreign car. chopped two feet out of the axle and welded it back together. Then added two 2x6's parallel to the wheels and sitting where the springs used to be and fastened them with "u" bolts. Then added two more 2x6's perpendicular to the first two and a handle, done. It cost approximately $50 to make.
If I can find time to modify it I would probably shorten the axle another foot or so. I also removed all the brake parts.