There is really no answer to this question, these cars are all old
enough now that mileage is virtually irrelevant, as well as motors and
drivetrain components are cheap and plentiful. What you want to look for
is condition, particularly of the body and other parts that are not
easily replaceable. I would take a car in really nice cosmetic shape, no
rust, with a half million miles and completely trashed motor over one
with 50K but mediocre body any day hands down. It's easy to change a
motor, but bodywork and a good paint job will cost a fortune and may
never be quite right.
As far as life expectancy of the motors, the one in my mom's '86 which
was bought new and has never been opened up is pushing up on 300K and
runs very well despite years of neglect back when it had become a bit of
a beater, and I've heard of several that had passed 400K, though I've
also seen a few that were tired after 120K. Too many factors to predict,
it's like predicting your own lifespan.
That said, for 400 bucks what do you expect? That's essentially zero as
far as cars go, you will spend more than that fixing up even a generally
well maintained old car to reliable daily driver status.
