In reference to my last post, this is the playlist I mentioned that I ended up with 40k despite ending up last overall. It does take some time and the Gumball rally map you'll need to be wary for moments where they troll you. Especially when the last checkpoint appears on your minimap. Pause the game and set a waypoint to it, otherwise you could end up in trouble. Also, it'll take a while to play all these races, so make sure you free up a couple of hours.
If you want something a little shorter, here's my playlist. Only once race is my own, the rest are longer races that I got from the above. It should also get a decent payout if playing with a few people.
Finally, if you want to try some of these out I'm trying to get some friends together on Friday night. We're all in the UK, so should be around from 8ish GMT. Just let me know your GT and I'll add you.
Buy a 10 car garage/apartment as soon as possible. There's one next to the eastern most mod shop. Grab as many Ballers or Felons you can fit. Then gradually sell them off, all the while looking out for more to keep it stocked. Easy way to make a quick $9000.