This is an interesting topic, as we'll be repairing at least one bathroom, and installing a whole new full bath.
I know the quote you mention is for a half bath, but my brief research online seemed to indicate the average bathroom install(entirely new) was around $15,000.
Of course, as an average, this takes into account many of the huge modern "spa" bathrooms we see in new construction, as that seems to be the trend. So that probably skews the average upwards.
I am certainly hoping that our new bathroom addition, which will be a conversion of an exiting large closet space(called the trunk closet in our floor-plan), will be significantly less. But I guess we'll see.
In the meantime, until I know different, I am budgeting $15k
We'll close on the house on the 17th, then we'll know more in a few weeks I suspect.