Just leave this link as it explains everything:
We all have read some comments in the subreddit about it's quite hard making money in the game, properties are not very profitable, and the missions that affect the stock market seem to be too few and too early.
I think I might have found why. When you open the store section in the pause menu, it says there is nothing available yet, but the console requests this file.
It's a plain XML file where you will see that besides of the downlodable content from the special editions, there are 4 so-called "cash cards", ranging from $100,000 to $1,250,000.
Its now more or less official as those were found on the R* Servers:
Plus a comment from that files:
Cash is king in this town. Solve your money problems and help get what you want across Los Santos and Blaine County with the purchase of cash packs for Grand Theft Auto Online. All purchased cash is automatically deposited into your character’s bank account. Spend wisely, cash therapy is fleeting.
It seems possible that this will also be available for GTAV SP as many complain that they dont have enough money to buy the Golf CLub for example, even when they finished the story. Nowhere near that number apparently...
I dont like this. Unless its only a shortcut Im fine but it looks like you will need that money. Otherwise you will have to play ages which gives this whole thing a F2P taste....