I've been wanting this book set and it has been hovering around the $60 mark until this deal emerged. From memory the last time it was this cheap was in the Big W pre-Christmas sale and sold out quick at this price point.
It's also available on eBay for anyone with coupons and/or eBay Plus.
Edit: eBay stock has sold out. Still appears available in some stores.
Edit 2: Picked up my copy and it has a different appearance to what is pictured on the Big W website and eBay. It actually looks like this: