Cost of expanding a window

We are allowed to replace existing windows in our apartment on the rear of the building and are thinking of replacing three windows that are currently 41"X82" with new ones that are 72"x82". This will require some of the bricks to be removed etc. Does anyone have a sense for how much such a renovation would cost? We are on the 9th floor and the building has 12 floors. another apartment in our building did similar changes and we were told that the workers came down from the top using a hanging work platform. The owner of that building is out of the country and we have not been able to talk to him or his contractor.