I'm not sure if it is, but that sounds like your best bet. Actually I just went back and checked and it looks like I misread the schedule. The last bus TO Fortuna leaves SJ at 11:30AM. So that can be totally ruled out. The 12:45 and 2:45PM departure times were for the return trip FROM Fortuna to SJ. Ooops

Anyway, even if there were an afternoon bus at 2:45, it would have been hard if not impossible to catch it if you don't get in until 2 and it would pass back by the airport around the same time as the shuttle. So it is well worth the $25 bucks anyway just to have it worked out ahead of time, be comfortable and not have to worry about anything. As far as local color is concerned, you can always catch that on the return trip when your timing will be much more flexible and I'm pretty sure I got those departure times right this time.