All the ways to make money in this game are boring, the fun ways only give you 1 or 2k and it would take forever to make a decent amount of money. (500k at least).
The fastest ways to earn some cash are :
Replaying RR over, and over, and over and over again, of course this is a f*cking boring sh*tty mission once you play it more than one time fun mission to do.
Selling Cars, findning the car Simeon wants. This is really boring... I don't see what could be fun about driving slow ass cars to LSC, or trying to find some ugly cars that nobody would want. (Fathom FQ2, oh my god it's so f*cking gross)
Playing survival, 20k.. but it takes forever, and nobody does it since everybody it's grinding RR all day.
Or you can just pray for the armored trucks glitch to make like 40k fast..
Well, but the funny things to do. pays you sh*t, or are in FR, so NO MONEY, but it'd be nice to be blowing up some PV's to the guys who are griefing you, without ending in bad sports. except for blowing up pv's, that's not funny.