Fly from San Francisco to San Jose, Costa Rica for $327 round-trip on Copa. This fare is widely available throughout the year. If you'd rather fly on US carriers American, Delta, or United, they are all selling tickets for $339 round-trip.
I was able to find seats departing San Francisco SFO this Friday, April 27, returning from San Jose SJO on Saturday, May 5. Flights connect in Panama City PTY. Other dates are available for travel throughout the year.
An excellent fare on a great airline. Copa includes two free checked bags in all of their fares. There is no advance purchase required, so you can leave tonight if you wish. I am flying to Costa Rica from LAX tonight. Maybe I'll see you there!
Need a room in San Jose, Costa Rica? Here's what's available for the above dates on Hotelwatchdog.