Wah! That depends on what wheels u trading in for.. if you taking the 19" BMW Performance wheels, they probably trade in yours for RM3~4k. Another option is to get the shop to sell for u, if they willing, honest and want your business la. Of course in the above case, the E90 has done more than RM40k of mods in the shop la. So the shop boss very willing to help the E90 owner out.
I also know someone who bought the 320i MSport staggered rim for RM600 [for 4 pcs] from a tyre shop and installed in his E36, using non stagger tyres.