Berlin has many hotels and guest houses at reasonable fees.
Room reservations should be made early, since July is a busy month with lots of tourists.
The public transportation system in Berlin is excellent and at reasonable fare, one way regardless of distance is 2.70 EUR.
You can take a hotel also at some distance from the conference site. Just make sure it is close to a subway or S-Bahn station.
see link: Berlin public transportation Tickets
Participants who want to be at a very comfortable place close to the conference site can book a guestroom at Seminaris Campushotel (see link)
A small number of rooms have been reserved for that purpose.
The Freie University of Berlin gets special conditions. When you make a reservation mention the keyword “PEB 2016” to obtain these conditions. The room fee will be 80.- EUR per night including a breakfast (which is actually excellent).