An average price for a standard room in hotels near Kazan University is 2000-3000 rub/night (about 50-70 euro/night).
An average price for a bed in the dormitory of the Kazan University (2-4 beds in room) is 450-700 rub/night (about 10-20 euro/night).
There are some hostels quite close to the university. The price for a bed is 600-900 rub/night (about 15-20 euro/night).
Hotel «Hayall», the price is in roubles per night (only for the conference participants)
Hotel «Ibis», the price is in roubles per night (only for the conference participants)
Please note that it's better to book a room in advance (about 1.5-2 months).
The following webpage also could be useful http://www.kazan-hotel.ru/ (it doesn't have an English version, so "google translation" helps). It has a booking information about all main hotels in Kazan.