Before my Mustachian days I bought my wife a Toyota Sequoia. $45K. A few weeks ago I bought my son a beautiful car, and I mean really nice, for $800. The car was owned by this old lady and the other seats had hardly ever been sat on.
Doing the math, that's 56 cars instead of the Sequoia. I'm sure I probably couldn't get as good a deal on the next 55 cars, but did I ever learn my lesson.
My dad used to say, "When you buy a used car, you're buying someone else's problems". Nowadays, with the way cars are made, I don't think that statement is true.
On the payback of the student loan debt, I hate owing others too, but this one seems like a no brainer, though sounds like wife would have to be committed for 5 years. Is that something she wants or might another teaching job open that would be closer to home with greater pay? Then it could be in your best interest to pay off loan at that time.
With a paid off economical used car, perhaps you could bump up your savings rate to 60%.