Serena Dai takes a stab:
The havoc Sandy is wrecking may cost some $20 billion in economic damage, according to risk firm Eqecat Inc. It's a lot of money—so much, in fact, that the costs places Sandy in the top 10 most expensive hurricanes ever. Comparing Sandy with numbers from the National Hurricane Center's top ten costliest hurricanes list, Sandy places sixth when numbers are adjusted to 2010 dollars. NHC combines insured loss with National Flood Insurance Program figures to calculate its list. Sandy's costs will include repairing the New York subway system and any wind and rain damage to buildings.
Jared Bernstein reframes the analysis:
I’ve seen rough loss estimates of around $20 billion, of which some (half?) will be replaced by insurance payouts. Though retail, as noted, will take a hit, demand for storm-preparedness goods spiked big time before Sandy hit. And many–not all–trips and activities that were cancelled before the storm will now take place afterwards.
And then there’s the difference between gross domestic product and net domestic product. When stuff gets destroyed in a storm, that subtracts from the economy’s net product, but if it’s replaced, it actually adds to gross product. One economist, Diane Swonk, estimates that Sandy will actually "add from two-tenths to half a percentage point to economic growth this quarter."
The Dish 