Car hire in Spain is just about the cheapest in the Western World. What's more, car rentals on the Costa Blanca are among the cheapest in Spain !
EDI Rentals is owned and run by British people and do rentals from Alicante Airport. All EDI cars have Air Conditioning and are inclusive of all taxes, insurance and are for 2 drivers. Petrol is not included and baby seats/boosters are EUR 6 per hire. This is a great service if you want to be sure of dealing with British people. Their website is at http://www.edirentacar.com.
Many websites also offer a good service. We have used the following and have experienced a good service :-
http://www.holidayautos.co.uk/