Based on what I think I’m reading your needs are, there might be an interesting option for you, and it’s one my family has bought into recently. Your concern doesn’t seem to be fuel efficiency directly, but more the running cost/mile. Which in the case of diesels, won’t buy you any cost benefit as their higher price/gallon reflects their inherent energy density advantage making it mostly a wash.
I think you’re also saying that for extended trips, your family uses your husbands free fuel vehicle?
If that’s the case, the Toyota RAV4 EV might just fit your needs. It’s a joint venture between Tesla and Toyota…essentially a Tesla Model S drivetrain/battery adapted to a proven RAV4 chassis. It’s my wife’s DD and the weekend family runabout, and it’s way exceeded my expectations. From an efficiency standpoint, for the size vehicle, it cannot be beat. ‘Fueling’ costs are about 1/4-1/5 the cost of gasoline through the utility company. And maintenance costs are practically nil save for tires.
Just to give you a perspective, I had an ’05 4Runner V8, and the RAV4 easily eclipses that car in interior volume since you said that’s a factor. I have a LX470 that we use to use as the weekend car, and it’s use has been mostly displaced by the RAV. The unibody of the RAV lends it an inherent advantage in interior volume over body on frame vehicles like my LX470. Yes the LX is wider/roomier, but I was pleasantly surprised at the interior space offered by the RAV.
Along with what others have mentioned, I refuse to do tin can econo cars like the leaf/prius, as when push comes to shove in an accident, mass will win. The RAV4 EV is a legitimate sized vehicle, with the exact same tire fitments as the gas version, so safety is not compromised for the sake of efficiency.
As it’s the Tesla drivetrain, the RAV4 EV is shockingly performant – just about the fastest of all the EV production vehicles save for the Tesla models themselves. Easily a 6.9-7 sec 0-60, which is even faster than the V6 version of the RAV4. And it can go 100-140 miles depending on a standard charge or extended charge. Plenty for a runabout.
It’s a 49k car, but with huge incentives: $10k CA/Fed, $10k Toyota finance cash, and 0% 5yr financing. I got $10k in pocket before I even made practically any payments.
If you don’t need the car for long trips, I wholly recommend it. It’s even more awesome when it’s fueled by a solar system 😉