@Megs04 RAH do have a wigs library. It's run by the volunteers (previously known as the Lavender Ladies and Lads). I think it's only open on weekdays (9-4? but could be wrong about times). The deal is $25 for wig hire for as long as you need it. You get one exchange in that. They have lots of wigs but not a great deal of longer styles and they are lovely to deal with (Isobel fitted mine and she was so sweet). The volunteers (and the wig library) are situated just inside the main doors and tucked in to the right. I think the direct number is 7074 1246 but if I've got that wrong just dial the main switchboard and ask to speak to the volunteers. I think you do need to make an appointment but I had no trouble getting one for the time that suited me.
Wigs are horrendously expensive and might be a good investment if you are going to wear one all of the time but I certainly didn't.
Are you on the Adelaide BC facebook group? That may be another option - you could ask if anyone has one that they are no longer using but you do need to make sure that it will fit you. Unfortunately, I have already given mine away or you could have had it.