Costumes can be unlocked by completing Episodes and Sub-Missions with an AAA ranking. I'm unsure whether the lingerie that is unlocked for the Beauties counts towards this achievement, I don't think that they do. Once the costumes are unlocked there will be a lot of money grinding involved to be able to purchase them all. Good luck.
Money Grinding Method:
The easiest method (that I've found thus far) of accumulating money quickly is to set the game to Nightmare Mode and replay Episode 1. The Episode is 35-38 seconds long and will reward you with anywhere from $720,000-$729,000 money per play through on Nightmare Mode. REMEMBER TO UNEQUIP THE DARK BOOSTER AND ULTI-MONDO COSTUMES WHEN MONEY GRINDING.