This sounds harder than it actually is. Just keep in mind that all characters receive money and XB boni, regardless if you play them or not. My primary character was Kyoko, so hardly played and spent any money with Misako. For me, the trophy unlocked about at 80% of my "New Game+" run, when Misakos funds reached 5.000$
Notice however: Every time you get K.O.'d, you will loose HALF OF YOUR CURRENT MONEY AMOUNT. However, you can avoid this by exiting and restarting the game via the dashboard BEFORE you respawn and continue playing.