The city of Utrecht is very compact, so most hotels are within walking distance of the venues and are near to the Central Station and bus connections.
There are many nice hotels and B&Bs located in the old city centre. Youth hostels are of course cheaper as hotels, but can have several beds to a room. See below for several options:
Court Hotel City Centre Utrecht
Korte Nieuwstraat 14
5* hotel: Grand Hotel Karel V
Stay Okay Hostel Utrecht Centrum
Mitland Hotel Utrecht