From Wikipedia: http://en.wikipedia.org/wiki/Hotel_Bossert
Purchase by Watchtower and restoration
In 1983, the Watchtower Bible and Tract Society of New York began leasing space in the Bossert for use byJehovah's Witnesses. The Society bought the hotel in 1988. It required extensive restoration according to the Landmarks Preservation Commission standards for the historic district. The famed Marine Roof had collapsed, and a new roof had to be built. Also, the lobby was in poor condition, and over 2,500 square feet (230 m 2 ) of the marble had to be replaced. Watchtower went to the original quarry to replace it. [2] That effort garnered praise and awards. [5]
In late January 2008, the Society announced it would sell the building. [1] The sale will be conducted through a private-bidding process, which could take months. [5] One local realtor (Arlene Waye of Awaye Realty) estimated that the building would sell for about $100 million. [2] Judi Stanton, the president of the Brooklyn Heights Association, remarked that “The Witnesses have done an exquisite job in maintaining the building." [5] Timothy King, a senior partner at Massey Knakal Realty Services Brooklyn, agreed calling the hotel "one of the most unique and most well-maintained trophy assets in Brooklyn." He continued, "The Watchtower organization is well known for impeccable maintenance standards and the Bossert reflects this level of care. It will be a challenge for a new owner to run the building with the same level of care and attention to detail." [2]
Late in 2012, the Bossert was sold to David Bistricer of Clipper Equity and the Chetrit Group, who plans to turn it into a boutique hotel with around 300 rooms
Would need a little more research to find out that 1988 purchase price - EDIT - undisclosed purchase price according to the NY Times