There are two payments you can get (if working for the Federal government) one is Per Diem, meaning that you get a daily allowance for Meals, Lodging, and Incidental expenses. This varies by location, and sometimes the season.
If deployed to a no kidding combat zone, then you can get hazardous duty pay of anywhere from $150 to $250 for a month. But it is a pittance compared to what contractors receive.
A contractor that is in say Iraq or Afghanistan will receive quaranteed overtime (some as much as regular salary, add 30 additional work hours, and then then add a 70% danger bonus. KBR has taken homeless people off the street in Houston who are now making $75K a year tax-free, with free lodging and meals, just to hand out bottled water and gatoraide in the galley's. Not bad for unskilled labor.)
Most goverment contractors going on short-term travel will use government per diem rates. Those rates can be checked at
http://www.dfas.mil
have fun on your trip.