After your first year in Fight To The Top mode, you should have enough money to buy a team. Buy a team, then go to get a sponsorship. Accept the one with the best signing bonus, then go back to team management and sell the team. It will be worth the same amount of money as you bought it. This works best with a team with low prestige, as they will get less money per race but more as a signing bonus. You can do this as many times as desired.