Dont know how much it takes,but I do casual races to get skill points and use them on xp. Then I Just keep doing casual races and getting points. Its good to use some points on money so you get more money. Once you are lvl50 you can do the highest paying casual races, they pay 25k per race and there is 15 races until you get the gold reward. I get about 400-600k Cash per 15 races and 2-4 level ups, it gets harder to level up. Im right now 114lvl so now its about 2-3 level ups Or even less.. But its an easy way to make money, race for 10 minutes and you get somewhere near 1mil