You cant go wrong either way with Prius or Civic. At 140miles/day and getting 50mpg+ versus 24mpg now you will be saving on fuel.

I got the cheapo Civic without Nav bu the mp3 jack makes it ok as does multi format cd player and xm radio. Need a key to start it.

If you can stay at 65mph, I bet you will still get 50-55mpg on those stretches. AC will hurt this a little.