I think I posted a price of £495 plus p&p for the parallel arms on the RST section a while back.
Jano - just remember you WILL need coilovers on the rear though to run this type of set up, which is why we develop and make the Bilstein stuff in conjunction.
We also do a fully adjustable rear tie bar to complete the ultimate in adjustable rear set-ups. This full set-up gets rid of all the rubber bushes on the back end, and the difference is remarkable.
All of our items are developed on track and rally events over time with alot of testing to get them right. As such constant mods are always being looked at to eeeek out more performance.

Tony