Weekly Events
Probably the best approach to make cash fast in GTA V is to participate in Rockstar's weekly double money events. They refresh every Thursday and can add to your bank account pretty quickly. You should also try looking for limited-time discount offers on properties, businesses, vehicles, etc. If you really want to go on a spending spree in GTA V, there's no better time to do so than these events.
Gunrunning
Gunrunning is the best passive income you're going to find in GTA Online. It requires a bunker, which costs a minimum of $1.2 million. Once you purchase one, go ahead and start manufacturing the weapons. Keep checking in on the current progress with the SecuroServ app. Once you start selling from your bunker, you can probably make up to $80,000 per hour passively.
Heists
Heists are the most fun way to earn money in the game. If you have a group of friends that own the game, you're going to have a lot of fun while earning mad cash while doing so. One of your friends needs to have a high-end apartment, and you can start making money. It'll be a bit difficult at the start when you're still figuring things out. Once you've done a couple of successful heists, you should probably be able to speed run through them without much issue. The Pacific Standard Heist is probably the best heist you can do. The Doomsday Heist is also a good idea, but it'll require a more expensive facility, which you might not have. The individual take from a single heist ranges anywhere from $600,000 to $1 million.
