If you are low on cash, just defeat one of the opponents on the black-list. You will get two marks to use on several different things. Do not use them on the Uniques early in the game. Instead, use them on the middle or the left 'Random' choices. They should always come out to either be a big cash bonus or the opponent's pink slip.

Because you can repeat blacklist races you have completed and still earn money for it, do any of Kaze's tollbooth races. You will get $10,000 for winning. By this point in the game you should have hopefully obtained the Porsche Cayenne from Baron. If not, your fastest car should do fine.