First, the per diem deduction (a.k.a. M&IE expenses) are simply one component of a flight crewmember's employee expenses that get itemized on a pilot or flight attendant's tax return.

To estimate the actual amount that a flight crewmember benefits from fully taking advantage of the flight crew tax deductions is complicated.  It depends on several factors. Assuming an effective tax rate of 20% and $2,000 in other employee deductions in addition to the employee expenses, the benefit (i.e. reduced tax liability) might average around $1,000.  Again, this a very rough approximation, but the amount is typically  significant, and EZPerDiem makes it very fast to calculate.