Auditions are one of the easiest events to hold. After all, you don't have much decorating to do. It's mostly about having a large, quiet space, with a performance space
for the auditioners and where the judges can observe. You do need to pay attention to lighting and sound quality especially if you intend on recording each audition. Otherwise, a school gym, theater, office building room, or library conference room can all work as an audition space to rent.
That said, when searching for an audition space to rent, don't forget about the amenities. Changing rooms are important if you expect actors to get into and out of costumes. Waiting rooms and cast lounges allow attendees to take calls, converse, and relax in comfort without disrupting the auditions on stage. Bathrooms and water fountains are important, as is parking that's free or at least conveniently located close to the audition venue. If parking is a hassle then seek a venue that's close to public transportation stops.