Commercial rents in Manhattan took a big nose dive in the first three months of this year. Cushman and Wakefield reports the six percent drop is the largest the company has seen since it started tracking commercial rents in the mid-80s. Joseph Harbert is chief operating officer for Cushman's metro region.

HARBERT: When you look at the past two recessions, it took that number of quarters, 11 quarters, to get down to the bottom, from the peak pricing to the trough. now we're kind of half way there in very few months.

Harbert is assuming rents will fall no more than 30 percent from their peak last fall. He says he expects Manhattan's commercial real estate market to hit bottom by the end of this year.