NFSUnlimited.net

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.

I found it while googling!