Well, this is a really simple unlimited money glitch after patch 1.35. With this simple trick you can do the Headhunter mission over and over again to gain millions of dollars. Minimum $280.000 per hour!
1. Start the VIP job called Headhunter
2. Once finished, find a new session
3. Wait 4 minutes and then start the mission again
4. Now you are able to repeat the mission as much as you want!