I find an easy way to earn consistent cash online without doing missions or races, is to find a decent car to sell to LS Customs for 8-9k (there's a list of cars and their values on the internet), then rob convenience stores for 1-6k while waiting the 48 minutes until you can sell another car to LSC (or you can do missions to kill the time). One LSC is right on a highway and you can just hang out the front stopping traffic til you get a good car, or visit the nearby redneck trailer park where there is usually good cars parked.
Arm wrestling is hilarious, I've only met one dude who can beat me. I cheat though, using my palm to move the thumb sticks instead of fingers.