We returned the rental car at the airport. Iguazu Rental Car charges an extra fee depending where you pick up or drop off. The airport wasn't the cheapest but it is the most convenient. It is about 15km from town. We paid cash up front for the car but when we got back we didn't fill the petrol plus we exceeded the included kilometers (400km); we had 830km. So we had to pay more cash when we returned the car. In particular the excess kilometers were expensive. Funny, they call the overage 'kilómetros accidente' - accidental kilometers.