Each participant need to book (and pay) his own accommodation. There are plenty of hotels in each category available at Heidelberg, however.
Click here to for an overview on hotel at Heidelberg http://www.heidelberg.de/hd,Len/300652.html
Convenient and moderately prized accommodation offer the so called ‘Gästehäuser’, for example those offered by the University which is located next to the Marsilius Kolleg, http://www.uni-heidelberg.de/institutions/guesthouses/index.html,
or operated by private operators:
Information on Heidelberg: For a general tourist Information on Heidelberg, see here http://www.heidelberg-marketing.de/en