Why would you want to buy used shocks? The shocks on your car are used and I assume that you want to replace them with better shocks. If you can't afford KYB, or Bilstien just get a set of monroe sensatracs they give a nice ride for a very low price.
FWIW & IMHO:
I did not to mean to imply that I would prefer KYBs over Bilsteins, I would only run Bilsteins. I have run KYBs before, though, and they are a great shock for the money, but not really in the same league as Bilsteins.