You can rent by the hour, day, or week. I've not tried it yet, but it looks like they do a $10 credit and I saw cars nearby for $5.50 or $6 an hour. GetAround   There is also a Hertz Rental car location in the hotel, so you can also save money by taking BART to and from the airport and just rent a car for a day or few that you really want one.    

Some photographs from this entry were not included in the recovered backups (1 files).