The nearest airport to Sassari is Aeroporto di Alghero
There are several car rental:
*Aiguarentacar[url=http://www.Aiguarentacar.it]]
*Avis[url=http://www.Avis.com[/url]]
*Autoeurope.com[http://www.Autoeurope.com[/url]
*Europcar[http://www.Europcar.com]