Couldn't get on myself, so I spent the time waiting for the game to fail to load browsing for tips on my laptop. Here's a few, if you enjoy a bit of grind:
Apparently the Gallivanter Baller gives you the biggest payout at Los Santos Customs. You have to wait 20+ minutes before dropping each one off, but you get 9 grand when you do. This is what it looks like: http://i.imgur.com/cBpcaYE.png
Gerald's "Meth'd Up" mission is infinitely repeatable, needs 2 people and takes 3-5 mins for 5k.
"What I do is load into a solo GTAO instance (Load story, start>Online>Play Online>Solo) Then head north of LS to that strip of road where there is a chop shop a shop you can hold up and a clothing store right next to each other, sell a car at the chop shop, rob the store, get 2 stars, drive 100 meters into the desert, watch the cops, get 200 points for evasion, and repeat. Every 20 or so, try and sell a car, get 5-9k per car every 20, and 1.5k every 3-4 minutes."