And So, as far as i understand, GTA 5 did so realistic, that even the money in it is never enough. Cheats for money, alas, I have not found, but the people was discovered a bug, which allows you to gain money, adding each time 12000.
Read full for details.
The secret is, to one place to dive into the ocean and on the bottom near the sunken airship will suitcase, and therein 12000. In general, it must be chosen, up, persist. And so a few times. Here's a video, where it demonstrated: https://www.youtube.com/watch?v=lv09_ay3nVQ.
Also, this and another way to get free of weapons described here http://www.videogamesblogger.com/2013/09/18/grand-theft-auto-5-money-cheats.htm