OK then. Cab helps a lot because you'd have to budget maybe a half hour to handle a rental car and take SFO AirTrain to your terminal. A cab can drop you off right there.
Depending on traffic you might be looking at about 40-45 minutes and maybe $55-60. Cabs to the airport aren't flat rate. The last time I took a cab to SFO was for $43, but that was in the early morning from Market Street when we figured out that BART wasn't going to get us there in time. You'll probably be dealing with more wait time at traffic lights and maybe 3 more miles than we dealt with. You'll be leaving around rush hour. If you need to get there 90 minutes before departure time, I'd say leave at about 4:40.