From the First Quarter 2008 Massey Knakal Sales Journal:
A ten-story storage building at 305 East 61st Street on the Upper East Side of Manhattan was sold... [for] $28,000,000. The nearly 50-foot-wide storage facility is located on the north side of East 61st Street at Second Avenue. Based on its current R8B zoning distinction, the property allows up to 24,849 square feet. However, the building is currently overbuilt with a total of 65,853 square feet above grade. It was delivered vacant at closing. The property sold for $425.19 per square foot to a Manhattan self-storage investor.
The segment of the Vanderbilt Yard at issue is 495' x 200', or 99,000 square feet, more than 50% larger than the Upper East Side site. If you multiply the Upper East Side price by 1.5, it comes out to $42 million.
The Upper East Side site only supports 65,853 square feet. The Atlantic Yards arena block, of which this segment (Block 1119, Lot 7) would be at least a third, would support an 800,000 square foot arena and at least 1.5 million in development rights, according to the City Funding Agreement. (The towers on the area block, as approved, were supposed to contain 2.69 million square feet.)