The Small Cash Booster doubles the amount of you get for the next 5 matches. It costs 10 . It is a useful upgrade if you wish to stock up on cash. When it's in effect, you should see that your cash display is flashing green. It is the only kind of cash booster that can be dropped by elite enemy bosses in mission mode. The more useful ones are the Medium Cash Booster and the Big Cash Booster.