Deals for new buildings this year have commanded much higher prices. In January, Wafra Investment Advisory Group Inc., an arm of Kuwait's social-security agency, bought 2 Cooper Square in the Noho neighborhood for $134.1 million, or $993,403 per unit, according to Real Capital and New York City records. The capitalization rate -- a property's net income divided by the purchase price -- was 3.5 percent, the data firm said.

The 144-unit tower, which was completed in 2010, was Wafra's first residential acquisition in Manhattan, according to Harmon, who brokered the deal.

UDR, the third-largest U.S. apartment real estate investment trust, and MetLife Inc. in January bought the five- tower Columbus Square complex on the Upper West Side for about $630 million. It was the fifth multifamily deal in the borough for Highlands Ranch, Colorado-based UDR, which estimates the transaction at $887,000 per unit, according to Harry Alcock, senior vice president of asset management.

The price for the complex, which began leasing in 2009, "was really just driven by the profitability of the apartment building," Alcock said.

Columbus Square was acquired at an estimated initial cap rate of 3.9 percent, said Mark Biffert, senior REIT analyst at Bloomberg Industries. UDR estimates it can increase the yield to 4.5 percent over the next 12 months as the property becomes stabilized with 95 percent occupancy, higher market rents and the elimination of leasing concessions typical for new buildings, such as a month's free rent, according to Biffert's report on the deal.

Rent Increases

In UDR's four other Manhattan properties, leases are being renewed at average rents that are 9 percent to 14 percent higher than a year earlier, Alcock said. New agreements are commanding rates that are 9 percent to 13 percent more. The buildings are 97 percent occupied.

The company, which entered the New York market last year, owns about $1.5 billion of assets in the borough and "would be comfortable" adding others, even as limited deals draw more competitors, Alcock said.

"It's not obvious to me that values have moved to a point where we simply will not be able to invest," he said. "When you have a market where vacancies are so low, we just know we're going to continue to move rents."

About 3,000 new apartments are expected to be built in Manhattan within the next three years, the same as the annual average for the past 15 years, according to Leibowitz of CBRE.