This trophy is accumulative so you do not need to have $1,000,000 on hand for this to unlock. You can track the amount you've currently accumulated by checking the challenge "The Rich Get Richer." Challenges can be found on your quest menu as a sub-menu.
The most active way to getting money is to pick it up everywhere you go (lockers, piles, etc.). Additionally, selling all items (the higher the quality, the more it will sell for) is a good idea as well. This will come naturally as you play through the game so I would not worry if you do not pick up everything along the way all the time. It should unlock by the time you finish Playthrough 1.
Happy Hunting :)