Thanks for the responses.
Not a CAS booking, though I was offered a CAS discount after booking, 20% off the base rate. I queried it several times, being a long cheap fare already, the admin fees were going to cost more than the discount. The representative kept assuring me that it would be cheaper, but refused to put any actual numbers to it before I'd agree to them taking over the booking - terrible communication in general too. So no, I made it clear I wasn't interested.
We'll see if I can get an answer via the Australian phone numbers, but they may not love it being booked in USD.