i just sold my 2005 toyota matrix for about $7k, but it was in really exceedingly good shape and had fairly low mileage (despite having been to the playa once).
it was an amazing car. it took 3 people and all our stuff to the playa and back from indiana (including a costco barn strapped to the top). it got 32mpg highway and 25-28mpg city.
i miss it terribly but i traded up to a big toyota sienna, which took me to the playa this year. not as good on gas mileage (probably closer to 25mpg highway), but lots more room - makes for a better 36-hour drive.