From 1st April, 2009 ( this is not an April Fool's joke btw) Spanish Car Hire operator Auriga Crown
( http://www.aurigacrown.com ) have opened a desk at Faro Airport in the Algarve, Portugal
I talked with the ladies on the Auriga Crown desk at Faro Airport last week and they advised me that the company is offering one - way Spain to Faro, Algarve, Portugal drop-offs and vice-versa for only a € 30.00 premium.
In principle, this means you could pick up one of their cars at any of their offices in Spain and drop it of at Faro Airport and vice versa.