Slushboxes do amazingly well on the highway. The previous owner of my car said he got 36+ MPG's on an all highway trip, using cruise control and speeding most of the time (between 79 and 84 mph).
I'm getting close to beating that in mixed driving, but we'll see. If I were you, I would strongly look into the Fit, since it is very similar to my Civic, and within the same price range. There are tons of used ones in my area for under $10,000. Only problem is there are a lot more auto's than manuals, which is unfortunate. But get whatever fits your needs.
