Matrix/Vibe is a really good suggestion. Not the sport model. It's essentially a Corolla under the skin, so frugal & reliable.
I'm sure there are other wagon-y or hatchback types that can get 30-40 mpg highway. I'd recommend a 2nd gen Prius (50 mpg & bullet proof reliable and surprising room in back), but you'd be hard pressed to find one at that price.
Golf TDI (diesel) comes to mind too, but I'm not up on the VW reliability question.
I'm sure others will chime in with advice. I'll add a few words to your thread title to bring in some more eyeballs.
EDIT: never mind - I see you started a new thread asking for advice:
http://ecomodder.com/forum/showthrea...-6k-22778.html