I sold my Ford F250 Superduty Diesel (17/19 mpg), wiped out $14K of auto loan debt, and released $2K in equity which I directed immediately to other debt. I bought a '99 Toyota Corolla with 136K mi. (30/30 mpg) for $3800. It's a real turd, but man, is it cheap to operate.
Useful info:
I got the prorated portion of my insurance premium returned to me from State Farm by calling and asking for it ($200 back, whoohoo).
I got the prorated portion of the vehicle registration fee (tag) back by going down to the DMV with my bill of sale and asking for a refund ($100 back, aww yeah).
I miss the truck a little bit. It was fun to drive, and it made awesome diesely noises, and it made certain tasks very easy, but that's not the Mustachian way. Is it?! Anyway, if I can do it, so can you.