Make them yourself.............. use reclaimed timber, buy all the bolts etc from somewhere like Screwfix & when completed give them a coat of preservative from Wilkinsons (it comes in brown, green & blue). The poles you can buy ready made & likewise the cups.
It's easy, honest, I made a set & apart from my time it didn't cost that much.
I bought a load from the BSJA suppliers in Farnborough in Hampshire..... cost about £3 a pole and a tenner for a wall, i already had the wings but they also had those.
The were a little on the old side, but did me very well and when I was told not to jump merlin again I sold them...... for the same price (2 years later).