I think a Civic would be a great start for you, easy to find in a standard trans, seats four, and will be much better on gas than the Grand Cherokee. I would stay away from the "sporty" models like the Si and SiR civics, they are geared lower and won't give as good of mileage.
I went from an already efficient Neon to an older Civic VX (king of the hill for MPG civics), and I couldn't be happier with my decision.
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