i went to 1.8 Legit million by grinding. Not so proud of it since i wasted a lot of time grinding the same bunch of missions. I bought a nice Stinger, fully customized it.
i spent almost a week on the game to get the car. And i was past level 120. Then my crew started glitching money and i had about 15 millions in no time. No more boring grind for me, i just do missions for fun.