There are seats still available for those dates on several Southwest flights in each direction--$79 each way, plus taxes and fees.

http://www.southwest.com

Unless something's changed since last year, you can apply the money to a different set of Southwest flights for no fee--but the price of the ticket could go up if a $79 deal isn't in effect at the time you change the flights. (Last year, I was able to cancel a trip that was supposed to begin the following day and apply the money to a reservation for flights later in the year--no charge.)

I think the $79 deal each way is part of a Southwest sale that continues until February 3rd, and (as usual) seats are limited. But as of a few minutes ago, seats were available on three different flights on March 11th going LAX-SEA and on seven different flights on March 28th going SEA-LAX.

Good luck! Sounds like people have responded with lots of options for less expensive flights...