The Hague has a nice youth hostel located in the city. Trams 1 and 16 stop very close and all go to the Convention Center.
The hostel, a historic building, has been completely renovated and the interior re-designed as a youth hostel with all modern facilities. There are 220 beds in total, in 2-, 4-, 5- and 8-bed rooms with showers and separate toilets.
Please note that there has been a change in the way a school books the accommodation at the Stayokay hostel. In the past all bookings for the week of the conference had to be made through THIMUN, but from this year on you must book your accommodation at the hostel directly with Stayokay.
For your bookings please go to: http://www.stayokay.com/en/hostel/den-haag