Consider yourself lucky. Quote from BMW China yesterday:
USD 2334 for 4 new 18" run-flats
Part 85452536580 (Bridgestone Potenza RE 050 A RFT)
Part 85452536362 (Bridgestone Potenza RE 050 A RFT)
But I wonder why they did not quote the latest gen RFT...
These RFT are listed for the M135i
Bridgestone Potenza S 001 RFT 225/40R18 88Y
Bridgestone Potenza S 001 RFT 245/35R18 88Y
Continental SportContact 5 SSR 225/40R18 88Y
Continental SportContact 5 SSR 245/35R18 88Y
Goodyear Eagle F1 Asymmetric 2 ROF 225/40R18 88Y
Goodyear Eagle F1 Asymmetric 2 ROF 245/35R18 88Y
Pirelli P Zero r-f 225/40R18 88Y
Pirelli P Zero r-f 245/35R18 88Y