Speaking as someone who's lived through Betsy (1965), Camille (1969) Andrew (1992, Louisiana), Ivan (2004) and Katrina (2005), it will be at least a year, probably two before the total cost of the storm is known. The early estimates are just that, estimates. Once they actually start repairs and reconstruction, the real costs will be evident.

As for insurance, it's going to be an interesting battle. Here along the Gulf Coast, insurance companies have engaged in a bit of chicanery where they get an engineering report on the damage and then go out and have someone change the report to show it was caused by flooding. That way they get off the hook for paying damages for the most part, since they don't (or generally won't) write policies that cover possible storm surge, just wind and incidental damage (a car flew into the roof). I know Allstate in Mississippi got badly caught doing that along with other insurance companies.