I figured this out.
My total earnings are a little over 800,000
Granted, I played like 6 hours straight yesterday, but the secret is this.
Start out with the cheapest car you can get (diahatsu x4) win the sunday cup to get a car, use it to beat the clubman cup, and DONT SPEND ANY MONEY.
Use the miata you get from clubman to dump all the horsepower mods on, stage 2 turbo and such. Run the second race in the gt championship (super speedway) At 10k per race, you will have enough to buy yourself a real car in like 6 races. (I bought the top skyline)