ICAT Damage Estimator, an online tool that lets you explore our historical database of normalized US hurricane losses. The IDE has a neat feature which allows you to select a current storm and overlay the projected path according to the current NHC official forecast (or underlying model runs) -- The IDE can then calculate damage from all storms that made landfall within that "cone." You can also select all storms that passed within X miles of Irene's present position and compare damage statistics on that basis.
Here are some numbers from the IDE and links to the sources:
For storms that made landfall within Irene's 5-day official forecast cone:
Average damage: ~$14 billion
Median damage: ~$3 billion
For storms that passed within 50 miles of Irene's latest position:
Average damage: ~$9.3 billion
Median damage: ~$3.6 billion
I'll provide updates this week, meantime, please explore the tool yourself - ICAT Damage Estimator.