Doorway fans
You can buy inexpensive doorway fans that mount up in either corner of a doorway or hallway sill. The housing is triangular so you don't lose much "headway" space at all, even if you are real tall.
With that said, if it could work, floor vents and grates for the win! Look at all the old houses that used wood or coal, that is how they did it, no electricity needed. It isn't *that* hard to cut a hole in the floor/ceiling, and the grates have a trim piece to hide your cuts. About the only thing to check is electrical lines or floor joists or plumbing pipes whatever, try to miss those things when doing your cuts....good thing to know where all that stuff is anyway, map your house.