Go to location 1 and location 2 in the Pacific Ocean on the western side of the map with two different characters (Franklin and Michael are used in this example). There are briefcases in each location worth $34,000 total, and they respawn each time you switch between characters. Once one character is in the first spot, move the second character to the other location. Then, swim down to the briefcase and collect it, switch to the other character, swim down to the other briefcase and collect it, then switch back to the first character. Repeat this process as many times as desired to get an unlimited amount of money. You can get $1 million approximately every ten minutes. Each time you switch between characters, your oxygen will also be fully restored. This money exploit can be used with any two briefcases in the ocean. Note: Do not quick save the game while doing this money exploit, or it will start your character back at his house.