Before going for the 17" BMW package I checked on some E90 alloys on ebay a few months ago. . .looked like a good plan, then recently when I was actually looking to buy I noticed they'd all been bought up!
So either I went with 18" winter tyres. . $$$$$$ or 17" on BMW steel rims,
Didn't turn out too bad after all. . .in fact it rides better as well lol.