I just redid mine, worked out a trade so we didn't have to come out of pocket, but the original quote was about 25k, but
that didn't include the shower glass, vanity, mirror, fixtures, or tile, so your quote sounds about right. It is also smaller than 300 square feet. This quote also included removing two large windows and putting in a normal bathroom window. Whoever built this house and thought putting giant windows in the first floor master bathroom wasn't the brightest.