mk 4 astra 2000. Ignition circuit. HELP !!!!?

I am told that the ignition circuit has gone on my astra.I checked the wiring diagram and this looks like the problem. I am also led to believe that these cost £300 new, as the car does not warrent that kind of money plus labour, is it possible to buy second hand, get one myself from a scrap yard, and fit it myself. and what am i looking for ????