Look for a set of 18s (real OEM style 219.) There are always some for sale in the classifieds. Price for wheels only generally ranges from $800-1000 give or take for good condition, $1100-1300 with tires.
08 E90 | Jet Black / Black | 6MT
Mods: RAC RG63 w/ Pirelli Corsa 255F/285R | Akrapovic Evo Exhaust | OEM Blacklines
Winter Setup: OEM 18s w/ Nokian Hakkapeliita R 245/40-18