Someone that is going to come in and knock your socks off will probably expect you to have jobs booked in advance. If you don't, you're most likely only going to get "novices". Provide the PA for the audition. If you are lucky enough to find a "novice" that can actually sing well, figure out how to work with him/her and worry about the PA later. If you don't have any jobs, you won't need a PA.