There is no code for Need For Speed Undercover which grants the player unlimited money. However, there are cheats that can grant a player some additional money, just not an unlimited amount.
Cheat CC says that entering the codes $EDSOC and %%$3/" in the secret codes menu can each give a player $10,000 of in-game money. The code S1D3K1CK gives a player $15,000 of in-game money. Each of these codes can only be used once, so they do not provide unlimited funds, but simply a one-time boost.