Bicycle Trailer

I tried to make it simple, easy to manufacture and install to a bicycle with a ordinary rear axis. The wheels of trailer are 20" in this variant. The costs for materials are maybe about 15$. But then must be added the the costs for the wheels, for the bending of tubes, for cutting the plates and profiles, for welding. I took the bicycle from https://grabcad.com/ueasakun.potirin-1 https://grabcad.com/library/bicycle-parking-v2-1