Quote for reversing direction of stairs

Badcat

We live in a 2 bed terrace with access to the bathroom via one of the bedrooms. We have been quoted £9500 to reverse the stairs, and build a small corridor to the bathroom. The work also includes removing a sloping ceiling above the stairs and restoring the original flat ceiling( which all the other houses in the street have) . Think quote is bit on the high side even for London...what would be a fair quote for the work? We also had another quote for £1150; not sure if this is a joke or the builder has forgotten a zero!
Thanks