I dont think the concern is about costs of changing or creating additional toilets.
Employers are terrified of the TRAs.
They are terrified there are going to be law suits, accusations of transphobia, mental health distress.
So even though on one level it is about reasonable, easy adjustment, that isn't they real problem.
The TRAs are in charge, and no one thinks women are important enought to take a stand for, even if the highest court in the land has told them that legally they should.