Tried another method with this achievement is more simple than you imagine :)
In the beginning don't buy too much, safe your money.
If you get in Career Mode an option with Shoes Sponsoring, select on Slappy Shop or Reel.
In the shop bring to Basement and Sponsor. Sign contract with Adidas. If you got this sponsor go to Adidas Shop in Downtown and all of it's clothes, shoes, accessories is now for free, so "buy" anything until achievement pops w/ easy 5G's :)