We simply use old tyres and birch trees for now. Tyres work well, as 1 tyre is elevated ground pole, 2 tyres make a small jump, 3 tyres is about 2 ft jump, 4 tyres higher. Ofc, depends on the size of the tyre, but they stack up well and poles fly off easy if knocked.
Also can build a "wall" from tyres.. At the moment for low jumps they work great. As I don't even need 3 ft jumps I simply work with the tyres and a few poles. Birch works great as its already white and bright