So, I am kind of an Insight groupie, but are you specifically looking for a NEW car? The way I read your post it seems like you need a new to YOU car, and want to spend the least amount of money/money per mile.
100% new, the Mirage is a great vehicle, but I'd suggest a Focus ST. 6 speed, fun if you ever want it, and easy great mileage in a good package. There are a lot of brand new, "older" models that people can't move because of the new ST, and RS coming out. Amazing deals on them, but it still costs 33% more than the Mirage- I'd argue it is 33% more car, and with the deal, will retain more value and have a better (relative) resale value.
If you want best cost per mile, used is the way to go. You could buy 2-3 Insights or Echo's for the price of a great deal on a Mirage, more with the Yaris H, and your cost per mile will never come close. I want to chime in with what is best for you in my opinion that fits your wants and needs, but I think we need a little more clarity.
Does it need to be brand new? How far will you travel? Any size/other requirements?