I just got this kit (I paid $55) and it came with a 15% off code. Came to post the code as a deal and noticed there is already a sale on the kits bringing them down to $40. Add the 15% and it gets you down to $34!
The kit seems to be decent quality, it's brewing at the moment so will know if it tastes good in 5 days. More products including an 8L kit here: https://karlkombucha.com.au/collections/all
I did a bunch of research on Aussie kombucha suppliers and this mob seemed to be one of the better value ones. Their main page has heaps of photos of happy customers taking photos of their brews, seems legit.