This will unlock as soon as you have $500,000 on hand. After a little while into the game, the missions become worth around $10,000 to $15,000 apiece. Also, when completing Brucie's email missions and Stevie's text message missions, the cars are worth more money if they are in good condition, so remember, as is mentioned in that section of the guide, Pay N' Spray your car before returning it to him. You can also perform odd jobs for people all over town, drive taxis, kill hookers, and other things that it just wouldn't be a GTA game without, to collect enough money to reach this lofty bankroll.
You will also receive $250,000 for completing the mission "Three Leaf Clover," as well as another $250,000 for the deal/revenge mission, so those two missions alone will net you the achievement.
**Can be done after completing story mode**