Are you talking "free" jumps?! Barrels, tyres, pallets (can put brush in them), doors, plastic containers, lots of stuff! If you're going to building wings and stuff make sure they are sturdy enough, it's so annoying if they fall over at the first gust of wind, and they will get wrecked too.
Make jump stands out of 3" x 2" tanalised softwood. I've made about 6 pairs now, and reckon they cost £12.50 a pair. including screws etc. As my carpentry isn't up to much I buy those 'L' shaped metal screw on jobs to fix the feet onto the stands.
Nailed together stands haven't lasted that well, but the ones I've screwed together are still going strong after 5yrs.
They look pretty crap but do the job well, and the taller the stand, the smaller I think the jump looks so mine are mostly 5ft tall (an optical illusion for a scaredy cat SJ'er!!)
Get some ready-cut 2'x4' ply from the orange DIY superstore (think it was 9mm) and paint both sides with gloss and a design. Using at least 4" x 3" timber (rough sawn will do) cut into 18" and 9" lengths. Make a 9mm groove to about 3/4 of the way through, in each one (cross ways, centre) and jam the painted ply down onto them. Longer foot to outside and shorter foot to inside. Two of these nicely fit under a 10'/3m fence. Paint the edges well and they will last years.