The South of Spain is well catered for by car rental companies and the competition helps to keep prices down.
For the cheapest prices you are best off booking through one of the many online rental agencies such as carjet.
Spain's modern system of national highways and Autopistas (motorways) make it easily accessible to the rest of Europe and car rentals are very competitive, especially out of season. From the UK and Ireland it is easy to take a ferry or the Eurotunnel to France and then drive down, or take a ferry from the UK to the north of Spain and then drive down.