I have cheap bars from eBay and they are actually really strong and work. The reason they don't cost much is because there is no warranty, small company, probably not much quality control, and are an almost universal fit (pretty adjustable in several places). Mine don't have any quality defects, so the only problem I face is the fitment. They do fit perfectly, but the fact that they're adjustable makes proper installation a pain, and after enough use they'll start to loosen up. Tightening them back up is pretty quick and easy though, and they don't come loose fast at all.

For me, they were definately worth the $30-40 I spent for both the front and rear bars and they do make a noticable performance improvement. I don't know if the rear bar made much of a difference, but the front one did for sure. I actually went out and tested my speed through some curves before and after installation. It's certainly not as big of a difference as when I installed my Type-R rear sway bar, but it's still an undeniable improvement, none-the-less.