There would be rent consts for the room, as this is not an ETH event.
Furthermore it still depends on when exactly the conference would be
as it is strictly not possible to have it during the term, or during
the exam time. They said, when this is known more concrete
clarification could be done.
I think the best time would be July or August. It's during the
university holidays in most countries. November would be another option
if accomodation prices turn out to be lower. I don't think this would be
the case in Zurich.
So please ask for prices in July or August.