Each time you spend coins on extra moves on the same level, the cost goes up!
It costs 25 coins for the first time, 50 coins for the second time, 75 coins for the 3rd time, etc. for the same level.
Starting from the second extra moves spendings for the same level, you'll receive extra moves along with booster.
Planning a couple of moves ahead will help you out when you use the extra moves!