Insurance claims could top $7bn (£4.3bn), the Consumer Federation of America estimated.
The brunt of Irene's impact was felt by towns and suburbs from North Carolina to Vermont.
Driving rains and flood tides damaged homes and cut power to more than three million people in New Jersey, Connecticut and New York alone.
Further damage predicted The storm passed over the east coast at the weekend and has now moved over the border into Canada's north-eastern provinces.
In New York, which escaped the worst of Irene's fury, transport resumed on Monday.
But Governor Andrew Cuomo said dozens of bridges and roadways would need to be repaired and that some of the state's rivers had yet to crest from flooding.
"You're going see more damage before it starts to get better," he told reporters.
The states south of New York, where Irene struck at hurricane-strength on Saturday and Sunday have begun the arduous task of cleaning up, assessing the damage and counting the dead.
Vermont lashed In the rural state of Vermont, the last hit before Irene passed into Canada, the storm washed away bridges and swamped the town of Brattleboro.
- Celena Sylvestri, 20, drowned when her car filled with water on a flooded New Jersey road. She had called her boyfriend and 911 for help.
- A New York man was electrocuted when he tried to rescue a child on a street with downed power lines.
- Two men in Florida drowned as they tried to swim or surf rough waves.
- Seven people were crushed by falling trees in Pennsylvania and Virginia.
The storm caused a section of a ski lodge to collapse in the town of Killington, where as many as 300 people were stranded on Monday.
Connecticut Governor Daniel Malloy said on Monday that in his state more homes were without power as a result of the storm than at any other time in the state's modern history.
In many areas electricity will not be restored for the rest of the week, Mr Malloy added.
The Associated Press news agency reports that 37 people have been killed in 11 states, mostly because of falling trees, ocean waves, downed power lines and raging floods caused by the storm.
Claims for wind damage are expected to be one sixth of the total sum from Hurricane Katrina in 2005, and claims for flood damage one tenth, the Consumer Federation of America estimated.
As it moved north-east, Irene was downgraded to a tropical storm and then a post-tropical cyclone.
The National Hurricane Center in Miami said an increase in speed was expected over the next couple of days, with the centre of the storm moving over eastern Canada on Monday.
A tropical storm warning for Canada was likely to be lifted on Monday, it added.
Back to work The storm, downgraded from a hurricane, passed New York on Sunday.
More than 300,000 people evacuated from low-lying areas in New York City are now able to return home.
New Yorkers were back to work on Monday, with the city's subway network and its three main airports all reopened.
More than half the commuter rail lines running into the city were suspended or delayed amid lingering flooding and mudslides.
The US air transport network began slowly clearing a backlog after cancellations at the weekend. More than 1,400 flights were cancelled on Monday, according to Flightaware.com, compared with 7,804 on Sunday.
Airports in New York were worst hit by cancellations, but Philadelphia and Boston airports were also affected.
In Philadelphia, officials lifted the city's first state of emergency since 1986. Several buildings were destroyed by the storm, but there were no deaths or injuries.
Further south in North Carolina, Governor Beverly Perdue said some areas of the state were still unreachable. TV footage showed fallen trees and power lines.
Officials in Virginia have begun the clear-up, but say the damage was not as bad as feared.