Answer by taking a quote from the following article:

The Merchandise Mart (or the Merch Mart, or the Mart) is a commercial building located in the downtown Loop, of Chicago, Illinois, United States. When it opened in 1930, it was the largest building in the world, with 4,000,000 square feet (372,000 m2) of floor space. The art deco landmark is located at the junction of the Chicago River's branches. The building is a leading retailing and wholesale destination, hosting 20,000 visitors and tenants per day as of the late 2000s.

The Merchandise Mart was modernized in the late 1950s and 1960s. The Indian chiefs were removed and replaced with concrete plates in 1961, of minimal note to onlookers as skyscrapers did not rise on the north side of the river as predicted. Some of the carvings were later found in a suburban backyard and auctioned in 2014. In 1962, an entrance canopy was constructed over the south for vehicle use.  In 1977, Skidmore, Owings & Merrill designed the Chicago Apparel Center, located on the west side of Orleans Street, which increased the Merchandise Mart's total floor space to 6,200,000 square feet (580,000 m2). Making use of plazas, esplanades and overlooks employed the waterfront location for pedestrian pleasure. In 1988, Helmut Jahn designed an enclosed pedestrian walking bridge over Orleans Street connecting the Mart and the Apparel Center.  After a 10-year, $100 million modernization in the late 1980s that included public utility upgrades, Beyer Blinder Belle's commission in 1989 was to create additional perimeter entrances and restore the display windows, main entrance and lobby. On the south facade, the drive-through canopy was removed and two smaller doorways aside the main entrance were added. Display windows, painted over during the earlier modernization campaign, were restored with clear glass to showcase merchant's wares. New main and corner entrances were added to the rear facade, and the loading dock that occupied the north portion of the first floor of the river level was removed in order to use the bottom deck of North Bank Drive. Improvements to the lobby included restoration of the original glass curtain wall over the entrance, shop fronts and reception desk using terrazzo floors and wall sconces influenced by the original design. The project was completed in 1991.  In November 2007, the building received LEED for Existing Buildings Silver recognition.

How much did it cost?
After a 10-year, $100 million modernization in the late 1980s