If you already happen to play this horrible game here's a quick and unnecessary guide for you!
This guide will help you get max cash out of race simply by doing drifts for the whole race. Here's how to do this:

1. After starting any race press boost and drift buttion simultaneously and hold until the end of race.

2. Swing your steering left and right.

Make sure not to oversteer too much in one direction or you might bump into invisible wall.

3. Rinse and repeat.

After some practice you will be able to master the art of long curves...

4. Enjoy cash after completing the race!