You still pay all costs for that spell, including additional costs. You may also pay alternative costs, such as overload costs. Although you can’t pay additional costs for the copy that’s created, effects based on any additional costs that were paid for the original spell are copied as though those same costs were paid for the copy too. For example, if a player sacrifices a 3/3 creature to cast Fling, and you copy it, the copy of Fling will also deal 3 damage to its target.