How about starting with EPA, NIH, NPR, NEA, FCC,(the alphabet soup list is endless) then start looking at the multi-levels of unnecessary bureaucracies all through the federal government. Cutting ~40% of government is actually rather easy, without even touching on the necessities, such as national defense.Then make those cuts part of the bill, because right now the FairTax effectively cuts the budgets of every department equally, across the board.
That works for me as well. There are numerous levels of unnecessary bureaucrats throughout all of government, including defense that could easily be done away with.
Then when the necessities, such as national defense needs more, it can be taken from the others.