This achievement will require you to buy most of the more costly items in the game. After buying about everything in game I spent around $140,000. Most of the clothes aren't worth buying because they're cheaper than $100, so I'd focus on instruments. After you beat the 'story' you unlock golden versions of instruments for purchase. The Guitar and Bass are about $9000 each and the drums were $16000 or $18000. Buying all the Guitars and Basses should get you most if not all of what you still need after that.
Note: Moneyshot360 confirms that only the band creator gets the achievement.
Edit - While I didn't need to buy any, note that men and women have some separate clothing to buy.