The stands pictured function at least as well as free standing targets -- which have their own problems -- and are actually a little easier to spot on since the targets always fall straight back. If balanced and leveled properly, they work almost flawlessly; although we get an occasional bounce-back-up on chickens. Almost everyone who's shot on ours has been positive.
As for cost, IIRC we paid $150 per bank of five. (This was materials only -- you'll have to find someone who can weld and is willing to volunteer his time.)
We feel that that cost was certainly not prohibitive and the safety factor of not having people down range resetting is more than worth the money we spent...
Mongo, whose resets were you shooting on that didn't work well? (I'm told that the ones used in France at the last world matches were less than good.)
Chunter, if you're really cash-short, railroad iron rails work well and are almost indestructible. All you have to do is weld pads on top. (Since you have to move them, I'd think that a little engineering would produce wheeled rails that could be easily moved and the cost would be pretty low. Lay-down backers would complete the setup.)
There're a gabillion ways to make rails and anything solid and level will work. If you want, email me and I'll get you some pics this weekend of the other systems we use -- or still have in place from previously -- at our range. The problem you'll face is that anything light enough to be truly portable will likely be subject to impact/vibration falls.