Massdrop only collects the money after the drop has ended. If a drop is successful, each drop participant is charged the same prices based on the price point that was reached.
It is possible for a drop to end early, depending on the demand and supply. Therefore, it is highly advisable to make sure your payment method is valid throughout the duration of the drop to avoid any payment capture issues.
If a drop is not successful, the authorization hold will be released and your account will not be charged.