X 2 on everything being close to San Francisco, Between Shell, Wyndham, Worldmark and ? {not as familiar with other brands} there are several options that might create an opportunity for a timeshare rental for less than a week from an owner.
Consider picking up a rental car on the way out of San Francisco heading towards Napa
- Avoids airport concession mark ups
- Parking in San Francisco will run a minimum
if of $ 30 / day plus charges at various attractions $$$
- Make sure the drop fee doesn't cancel the savings
Either Airport can provide BART access into San Francisco, Oakland requires a shuttle bus transfer to the Bart Station
If at all possible book the return from Napa out of Oakland, driving from Napa to SFO Airport could be an issue since you will have to drive through downtown San Francisco to get there.