I had a quote from a UK Berk supplier for around £850 delivered for the full cat back system, I can let you have the details if you want? PM me on Babybmw mate.
Current: 2011 F20 120d SE
2010 Alpine White N55 135i 6MT, 2009 LMB LCI N54 135i - Cobb tuned!, 2010 F10 530d SE, 1986 E30 318i
1981 E21 320i Auto