If you want to hire an especially popular magician or illusionist, realize that these are people at the top of their game -- and they don't come cheap. Not only will you need a lot a money to entice them to perform for you, they'll need plenty of advance notice.
Most magicians need a lot of room to perform, and some time in advance to prepare the show. If other types of acts are to perform at your event before or after the magician, make sure you all get together to discuss the magician's staging requirement for before and after the show.