One of the main goals in Grand Theft Auto has always been to generate income. This may be hard to do. There are a number of gamers complaining that it is simply too hard to make money on Grand Theft Auto V. The properties players can buy costs up to $150,000,000. So where are you expected to get all that cash? In earlier missions you can invest (assassination missions) and that will bring you a pretty penny. You can also buy stock in a company then attack its competition, that will cause your stock to rise. Although that will only get you so far.
A file posted by '1880', a Reddit user may answer why cash is so hard to come by. In itself the lack of easy money means nothing but combine that with the fact that the store section of your console's pause menu requests this file. The file found on Rockstar's servers mentions special editions (such as the Atomic Blimp), but also what they call "cash cards". These cards range from $100,000 to $1,250,000.
What exactly does this mean? It means that at some point you may have the option to use real money to buy in game cash. This is not exactly a welcomed idea among the Grand Theft Auto fan base. But players can understand why this may be necessary.
Since this is unlike Rockstar, the Reddit user who posted the thread gives other possible explanations for the file, such as a sweepstake of some sort. But Grand Theft Auto Online is a new venture for Rockstar. So we have no idea what it will take sustain a game of such magnitude.
This is purely speculation at this point, a rumor. Rockstar or Take-Two have yet to confirm or deny this. Still it raises a question. Are you willing to part with real world money to further your in-game lifestyle? We may soon find out.