Almost every place accept U.S. dollars. The change is in soles, approximately 3.30 soles per a dollar. You can exchange in commercial banks or in the streets. For internal flights Aero Continente and Aerocondor are the main domestic carriers, and provide extensive coverage. Save money also for your return.
Public buses are the usual mode of transport over long distances.
They are fairly cheap, frequent and relatively comfortable, at least on major routes. Make sure to have your passport handy to be shown at police checkpoints. Armed robberies on minor routes may occur at night. Local buses are slow, cheap and crowded. Competition is high, so they will do anything to get you on it.