Just been in contact with Milltek. They have the full exahust system ready for the M3.
Stainless steel, full system, four 90mm pipes etc etc. Total price €1,121.
Slightly cheaper i think you will agree than Gruppe M and Remus.
Still waiting on a price to fit, but they indicated it would be no more than €200.
Booked in for the job to be done early september