Can you please confirm if we hire a car at the Airport of Porto are we allowed to drive into Spain at no extra cost?
Most suppliers do allow cross border to Spain. To learn about travel restrictions, look here:-
To view the CROSS BORDER or FERRY terms and conditions. At STEP2 of our 3 step online booking process, alongside the car photo of your choice, there is a link entitled “IMPORTANT INFORMATION”. Clicking on this link will open an additional smaller window, with the terms and conditions appertaining to that particular car/supplier. Look under TRAVEL RESTRICTIONS
Try a few different suppliers as each supplier/vehicle type may have a different cross border rule.