There are plenty of small hotels and pensions in Sandomierz.
A typical price for a single and double room varies between 40 and 80 euro.
For an extensive list with booking option please look at: http://www.booking.com/Sandomierz-Hotele
Recommended hotel (conference venue) - Hotel Sarmata - http://www.hotelsarmata.pl
Rooms in Hotel Sarmata for supported participants will be booked by Organisers.
Other participants have to book rooms individually either in this or other hotels.
Other hotels:
Mały Rzym (***) - http://www.malyrzym.pl
Hotel Pod Ciżemką (***) - http://www.hotelcizemka.pl/
Hotel Basztowy (***) - http://www.hotelbasztowy.pl
A very economic solution would be Hotel Turysta - http://sandomierz-nocleg.pl