The Oktoberfest normally ends - after the extension respectively addition of one day some years ago - on October 3rd. (Anniversary of German unification).
During the Oktoberfest not only some air fares but the prices of accommodation rise extremely (with some 3star hotels going to the 150 Euro+ range for one night).
So if you are able to avoid and not reallly a fan of the Oktoberfest it's better to travel some days later.