Go to your local supercheap/autobarn or where ever you go to get your car parts and ask. They should be able to get you what you want. I think last time I priced a whiteline one from autobarn they were between 150 and 200.
What's the difference between understeer and oversteer? Understeer is when the driver is scared. Oversteer is when the passenger is scared.
I got mine a few weeks ago from Pedders. ( bet no one could see that coming) Paid $200 for it. I guess if you shop around abit try those auto parts stores, tyre places and suspension specialist.
Im guessing its a matter of you get what you pay for. mine looks a lot solider in comparison to the one that is being sold on ebay which judging from the one in the picture looks like it wouldnt allow for the same stiffness as what the one I picked up would offer.