The Vienna University of Technology (TU Wien) has concluded agreements with hotels in the surroundings. The conference members can thereby take up reduced prices for the duration of the conference. The list of the hotels is here. The booking code is "2016.05.0106 Hotels-TU Kooperation".
Another low price option is the Stephanushaus maintained by the Benedictine Sisters. It serves primarily the priests of the Archdiocese of Vienna as a home. Free rooms are available for day guests. The Stephanushaus has a direct bus connection to the TU and is located in a 20 min walk distance.
For an economic accommodation it is recommended to book rooms as early as possible