Nothing beats a prius for the gas mileage, but I had one as a rental car for week, and I hated it. The best time I had "driving" that car was when I was filling it up to return it to the rental agency. Drove it all around all week & it was only something like $8 to fill up. It was a very uncomfortable car for me to drive--it feels like your perched on the seat, and for me, the car constantly switched between electric & gas, and would surge. I agree with others--you pay upfront for any gas savings, and eventually you'll get it back, but the upfront pricing isn't great for what you're really getting.
I drive a VW diesel jetta. It gets decent gas mileage--38 mpg over the last few tanks (about 50% highway, 50% city, with lots of stop & go, short trips). Supposed to last 500K miles--we'll see. Cost was $27,500 & included the first 36K of maintenance (oil changes, etc). I'm at 65K miles now & no issues besides getting new tires (at around 60K miles). Oil changes (and other maintenance) are more expensive at around $100, but it's good for 10K miles. I like my car--and prefer to drive if at all possible vs. flying, but the diesel isn't for everyone. I know I'll still be driving it 10 years from now, and maybe even 20 years.
My husbands sonic gets 38 mpg easy--and gasoline is cheaper than diesel usually. Cost was around $15K, and it was the last of the previous years vehicles. It's a smaller car, with only 4 cylinders, but you only notice it as you get on the interstate & need that quick burst of power (you get it from the sonic, but you can tell it's giving you all it's got). It's got almost as many perks as my much more expensive car--can't go too wrong with $15K for a car--as long as it last at least 5 years, that's $3K a year or less.
I've got a 5 year old daughter, usually all 3 of us carpool (for around 20 mile one-way commute) and no issues with either the Sonic or the Jetta for getting her in & out. The Jetta is every so slightly bigger than the sonic. She prefers to ride in the Jetta--not sure exactly why (probably because she thinks of it as a girl car...) As others have said, you almost can't go wrong with most of the new small cars--most will get 35+ miles per gallon & are very economical. You'll have to decide what else you need from the car to help narrow it down more
