I hate to be the one delivering bad news...You're probably not going to be happy with the travel time or the prices...
I know that I'm not.

If you were able to score a non-stop flight to Jamaica from SF. It would only be about 6 1/2 hours in the air. Unfortunately I have yet to find a non-stop flight to Montego Bay from SFO.

We are looking at 13 hours of travel time door to door for our next trip to Negril. That's because of a 5 hour layover and also factoring the 2 hours. 30 minutes to get to SFO and an hour + half to drive to Negril.

The price of a round trip ticket SFO to MoBay is about $450 to $650. The average price is about $510. (although there has been a strange spike in prices as of late. I hope that stabilizes). You basically pay a lot for short layovers and convenient arrival/departure times. Tickets go as high as 1,100 for that kind of luxury.

We always get the cheapest possible airline tickets available, which means red eye flights and long layovers. Sometimes Multiple stop overs. We're utterly exhausted when we arrive

I'm jealous of our southern sister, Los Angeles. They have Spirit Airlines and super cheap specials to Jamaica. San Francisco does not.

The cheapest airline carrier to Jamaica for us is Airtran and recently American Airlines.

We've always had a stop over in Atlanta, seems to be the fastest way to go. This time we're doing Miami, so we'll see.

The commute to JA is not a pretty one from San Francisco. I'm not gonna lie.
But IMHO I think San francisco is the best place to live in all of the United States of America. I had given up on the states and moved to Europe for four years... then I discovered SF. I love it here.
You'll meet some of the most tolerant, loving and happy people here. Beautiful victorian homes, a rich vibrant history and The most stunning views...
So it's easier when the vacation is over to come back home.