My 135's rears needed replacing and decided to go with non run-flats all round. As a result I have two Bridgestone Potenza RE050A 215/40 R18 RFT's for sale.
The tyres have never been punctured and have even wear with about 60% tread remaining. My tyre mechanic suggested should get another 10,000-15,000 kays out of them (depending on how spirited your driving style!).
Best price I could find new was $400 with local BMW dealer asking $700! Asking price is $130 each - I am based on the Northern Beaches, Sydney