Hint: Easy money:

Collecting the little information logos around the city gives you money. You will receive $25 for each one.
As soon as you start the game, ignore Rachel's request to go to the car lot. Instead, try to collect as many information icons as possible. This will give you that little extra money to start modding your car, and will save time as you do not have to look for them in your initially slow car. Also, enter the two races shown on your GPS (circuit and sprint races). Going in these two races will give you at least 500 points in the bank. You should receive a message to get to the car lot now. Do so, and continue playing the game.

Listen to the other racers that periodically talk to you. They will say a general location in the city where you can find hidden races not shown on the map that are worth $850 instead of the usual $300.

In the career mode menu, go to the world map. Select any race that has not been completed in any stage. Once the race has started, pause game play and restart. After you have won the race, a screen will appear showing you how many reputation points and how much bank you have won. You will then go to the menu that asks if you want to return to explore mode, restart, etc. When this appears choose "Return To Main Menu". You do not have to save the game. Then, just go back into the career menu and select the "World Map" option again. Choose another race that has not been completed and start it. If done correctly, all of the races in the world map will be against three Toyota Corollas or a mixture of Hummers, Escalades and Navigators. If you restart these races, you will always get money if you win.

When you start with Rachel's car, do not take it back immediately. Instead, do some outruns and races to get money. You will then have a boost of money when you get your own car.

In career mode, eventually you will get sponsored and there will be purple crosses on the map. If you go to them, they are usually a sponsored circuit race. If you win them, you will get $900.

Enter career mode and go down to the Burger King and Best Buy area. Drive around and look for a stone wall and alley by the town shops. Go into the alley and turn sharply to the right. There will be a parking lot where an opponent will be sitting. He will not be appear on your navigation map, nor will you. You can challenge this opponent to an easy outrun. He will always drive towards the stadium. After you beat him, return to the parking lot where two red info messages will appear. Get them for $25 each. After you collect them, go into a garage, shop, etc., and save the game. Then, go back to the parking lot. Five green money bags will be there. Collect them, jump to the garage (on the main menu screen) and return for five more. This will get you money much easier than racing.

You can earn big money in stage 5. Go to garage in any stage of career mode and go to the world map. You can participate in races from previous stages. If you race one, pause game play and restart the race. You will get a bigger bank than if you had waited until you were done with all the stages (up to $31,00 in stage 5).

Once you have completed the game and are taking a long time to get money, go to your garage and access the world map. Find events that you have not completed. The races that are not completed may have money waiting once you win the race.

Use the following trick to get more money for winning a race. Watch for races that are not marked on the map. They give you more money for winning than a regular race.