Most of you may know this one already but I thought I would share, just in case. *Android version
Log out of your facebook account so that you are racing as a guest. You will still need to be connected to the internet. It is best to have a fully upgraded car so that you can easily make a time that gets the 5k bonus. I'm not that good and I can do it :)
Go to a Time Trial. While you are a guest, you can race and get the group bonuses (1000-5000) each race. If you have 5 drive pips you can scoop up 25k or more, depending on which TT you select.
Example: Pure Stock Challenge with the Nissan Silva. The normal payout is 850, assuming your time is good enough to beat the bottom five groups. With the 5k bonus your payout is 5850 and you can do that up to five times.
This is handy to generate some cash on the side for quick upgrades, etc. Also, the longer the lap the higher the base payout is, so some TT's have base payouts of 2000 or more. So, you can rack up 40k or more with five pips.
Caveats: It doesn't always work on the first race. I have found that this does not work on all Time Trials, so start with the example race to make sure it works for you, then try others. You have to make a decent time, if not your bonus will be less or even no bonus. The 1.4 update means that if you go off-track, you lose the bonus.