Start by doing the special scavenger hunts that are available in free mode-Bounty Targets for Maude, the revolver Treasure Hunt and Los Santos Slasher-for a total of $250,00 each.Search the GTA wiki for the names of anything mentioned below to get more info.
Despite all these changes the best money making method is still the Cayo Perico heist, so for new players it's all about accumulating the $2.2 million needed to buy the Kosatka submarine that unlocks it.