This achievement is not cumulative; you must have $1,000,000 in the bank at one given time to unlock this achievement. If you do not have this achievement by the end of the game, simply load up the last chapter of Mission 8 "Wilder's Crib" and play through until you obtain the first $75,000 then press and select "restart from last saved checkpoint".
Locations of the money:
3 boxes in the room in which two soldiers burst from at the very beginning
2 boxes below you, turn around as you drop down straight infront of the room with 3 boxes.
Drop down to the right and collect the single box hiding in the alcove
Make your way to the other side of the stairs and collect the single box hiding in the alcove