khare on a mk3 the immobiliser is a separate box, not in the clocks. the mk4 has it built into the clocks. I dont think the mk3 immob box is compatible with mk4 ecus, but could be wrong.
you can deffo get an immob defeat done for cheaper than that though, few guys on ed38 mentioned they got it done for £80, I'll see if i can find the threads.
edit: ok after a quick look apparently AMD and Jabba sport can do it for you