I for one was able to figure out that this question pertained to Michigan, and I don't see the need to bust your chops about not posting your location. I looked at a map, and saw Michigan right away.
Back to your question. Is this a Federal, State, or local government job? There is typically an administrative office which can answer this question. Per diem is a non-taxable payment to cover gas, food, and lodging. It is not to pay for labor or skill. As such, it is generally not part of a prevailing wage package. But local and regional interpretations can vary.