You can compare it to your own market. Find the price for used STi suspension on rexnet or something, and compare it to the price for Koni/GC or any of the hit and miss JDM coilovers.

Here Konis are like $600 or something, and GC springs are like $250 or so. Plus you still have to do a lot of work to get it to mount up. Compare that to an average $200-300 for take offs, and some work to get the rears to bolt up. I think you can see why some of us are more interested in this idea.