There are no exploits to generate cash and get rich quick in GTA online. Rockstar, the company behind the game does an impressive job plugging any holes in a timely manner and banning anyone involved in the scam. So unless you are prepared to spend real money on Shark Cards and have GTA$ deposited into your bank account you will need to work hard for it.
The most efficient way to earn money early in the game is to get a job. Jobs can be fournd scattered all around the map but can be easily accessed by checking the Quick Jobs tab on your Cell Phone. Not only can you farm wealth by doing jobs you will also increase Stats, Rank and Reputation. Avoid dying during Jobs as this will incur hospital fees. Replaying jobs will only give you half as much of a payout than when you first completed them.
Survival Mode
When you have reached level 15 the ability to play Survival mode will become unlocked. These survival Missions are anywhere from 1-4 players and if you work as a team you can earn $20,000 each time you complete them. Even if you don't you will still earn $18,000 if you last until the 10th round. If you decide to participate in these missions make sure you buy food in order to restore your health and if you have money you can spend $5,000 to call Merryweather for support. The maps in survival mode are: Processed, Boneyard, Sandy Survival, Industrial Plant, Sawmill Plant, and Railyard.
Steal Cars
Stealing non-tracked cars and taking them to a Mod Shop will depending on the car give you a good return. SUV's in particular sell for good prices, the Gallivanter Baller for example can be sold for $9,000. One of the best areas to prowl for high-end but sellable cars is the Richman area. Remember though that you can only sell one car every in-game day.
Save Sonny’s Daughter – $60K
If you head to the northern part of Paleto Bay you will come across a random encounter where two men are about to kill a girl who is mob boss 'Sonny's' daughter. If you kill the two men and take the girl to where she wants to go (Vinewood) you will later receive a call from her and $60,000 will be wired to your account.
Drug Shootout - $100K
At the end of the track on the east side of Mount Chilidad a marijuana leaf icon will appear on the map to indicate a Weed Farm. If you mount an assault on the barn you will be able steal a case that contains $100,000 of drug money. You can return to this random Event every couple of in-game weeks to get some extra income.
Buy Property
Although they are expensive, investing in property can earn you a weekly income and is one of the best ways to clean stolen money.
GTA Weekends
Rockstar offers special Weekly Update bonuses. These Events are normally announced on Friday and give players the opportunity to earn Double RP and bonus cash.
Chop
Chop, Lamar and then Franklin's loyal dog can earn you money. As well as being good at attaking anyone who gets in the way he is also good for sniffing out treasure and other collectibles.