I'd say UA Shuttle is your best bet. Go to http://www.ual.com and plug in some dates and times. Prices vary, but the big determinant is how far out you book. I'm not sure if Sat night stay is required, but going there and back the same day definitely ups the price about $70. I sometimes book about a month in advance (the minimum for these fares may be 14 days?) and go SJC-LAX-SJC for not much more than $100 including taxes. It was $88 RT a couple of months ago.