When returning rental cars to Alicante Airport fFollow the signs for " Rental Cars" with all the car hire names on. You enter the airport on the and turn right towards the parking areas and you immediately come up to the sign - it is very easy to miss - It doesn't say return rentals.
Don't enter the main car park - you know you have done this if you have to take a ticket. If you do and even park in a space with their name on, the rental people make you exit the car park, pay the small amount of parking charges and then go all the way around again until you enter the correct car park. There are big multinationals like Hertz , Avis , etc. You can also use a brokerage site, to help consolidate your search: