When was the last time you built a levee with the money flowing through New Orleans first?

Seriously, from this document:

In August 2002, the Corps completed a reconnaissance study of whether to strengthen coastal Louisiana’s hurricane damage reduction projects, including the New Orleans projects, to protect against Category 4 and 5 storms. If implemented, coastal Louisiana would have the only Category 5 protection system in the country. The next step in the Corps’ project development process is a feasibility study. The feasibility study for this project was estimated to cost $8 million and take at least five years; construction would take another 10 to 20 years and $2.5 billion.

The average entire Corps of Engineers budget since the mid-90s has been $1.5 billion a year.

So yes, there is some concern that 3.1 billions may be a little high just to fix New Orleans' levees.