The Piggy Bank is a new feature in which you will generate a coin package and right answers as you answer questions correctly in the classic mode.
You will be able to get it at any time for USD 5.99, or USD 11.99 for the ad-free version. Bear in mind that, since the cost of the ad-free version is higher, so are the prizes you will receive.
Even though the price is as mentioned, it could vary depending on your country's currency.