$320 - Direct Flights to Cabo from San Francisco
This winter, Alaska Airlines and United Airlines are offering direct flights to Cabo San Lucas Mexico from San Francisco for $320 including all taxes and fees.
Flights leave on Friday morning and return either on Sunday or Monday afternoon.
You can also get one-stop flights that usually either stop in LA, Phoenix, or Dallas for $301, though sometimes with one-stop flights, airlines will re-route you to another city without warning, so paying an extra $20 for a direct flight is often times worth it.
When in Cabo, there is plenty of nightlife and restaurants, but one of the best activities is sports fishing. My suggestion would be to pack a day pack then walk into one of the fishing stores in downtown Cabo, and negotiate a fishing trip. You can often get a personal boat with a guide, equipment, and bate for about $150-200 US.
In terms of timing, for some reason, the middle week in February is a little more expensive, so if you can, try traveling in late January or late February or March.