Are there any good types of one-way glass that can be used in a
bathroom so that people from the outside cant see in, even at night?
No. 'One-way' glass requires that you are in an area that is darker than
the area that you are observing. The person on the darker side always gets
the view.


Is there something like a slightly obscured glass with a one way
coating that would do the job?
No.

What is an affordable compromise?

Window shade or shutters.