I got the stock 18" wheels with my 535i, sold them to a east coast guy here on the forums for $1000 bucks.
Bought the 19" rims and tires for $1900 with 200 miles on them from a forum member.
Total cost to go from boring stock 18" to 19" ----- $900 bucks. IMO that is the best way to go !!
2012 535i, April build, Space Grey, Oyster Interior, 19" M sport rims/tires, premium pkg, premium sound, side/top cameras, heated seats, comfort access, ceramic controls, OEM spoiler, painted front reflectors, 35% tint, rear Fog lights, coded to my liking.