I don't know of any NFI projects (terminals/accounts) that offer per diem. The company has a program called "subsistence pay." Basically, this is the $59/day that the IRS allows you to claim on your taxes for DOT meals. This is NOT extra pay, but for every route over 250 miles from your base you get $59/day in non-taxable income.
Example: You earned 400 for a two day trip. 2 days x $59 = $118. This would leave you with $282 reported to the IRS as taxable income.
You can opt out of this if you prefer the mess of trying to figure it out on your own at tax time. But why?
If you had 3 trips of $400 per week, you'd make $61200 taxable at 51 weeks (assuming 1 week vacation).
At $282 x 51, you'd have $43146 in taxable income.
According to the 2013 Turbo Tax TaxCaster for a single person with no kids or other deductions other than self:
At 61200, your tax liability would be $8899
At 43146, it would be $4571
That's $4328 in tax savings alone added to your annual salary.