My cavalier (base model 2.2L w/ aftermarket A/C) averages 28-30+mpg all around and if you accelerate slowly and don't rev it a lot along with only stopping when you have to you can manage 35+mpg. Though I have had some problems, they were all minor issues: front disk brakes warping once and water pump needed replacement at 258k. The car has lasted to 273,000 for probably less than 2 grand spent on repairs. It goes through it's tires fairly slowly (front at rated at 400 and rears are 550 I think...so they are definitely not sport tires). Keep in mind that my cavalier is only a 98 so age-specific wearing is a lot less prominent then say a 10 year old car with less than 200k. Also my car is pre-ecotec so I can't comment on the new revisions that the cavalier has had recently...though my dad's 2003 cavalier ls with 60k is doing quite well.
If you want even better gas mileage I would suggest a hybrid. My personal pic is the civic hybrid insight, but the prius is also supposed to be a great choice. The echo is also a decent choice, though it doesn't have quite as good gas mileage since it's not a hybrid.
One thing to keep in mind is that imports will cost more to repair and have a higher initial cost so even if the american counterpart requires slightly more maintenance it may very well be worth it to go domestic. I do like imports and they tend to have a higher build quality so it will be a lot more fun to sit in...though you seem to be a minimalist so you probably aren't hugely bothered by meager creature comforts.
The smaller car you get the smaller the tires will be generally and thus much less expensive whenever you need to get new ones. The same is true for brakes and many other parts that need regular/semi-regular replacement. Make sure you get a 4 cylinder (or 3 if you get an older geo metro/ suzuki firefly
) and not a 6 because parts that are cylinder specific (valves, pistons, etc) will cost 50% more to replace since there are 50% more cylinders; not that you would be likely to consider a 6 in the first place since you want good gas mileage.