If you end up slightly short of Avios for the entire trip, you can save some by not booking SYD-CBR on Avios but paying cash for the ticket.

Book this on the Qantas (or Virgin Australia) website and not through any other online channel. The reason is that you will then get (perfectly legitimate) access to the lowest fares, which are typically only sold locally. At the moment, for example, QF has a sale for SYD-CBR which is available for certain travel periods for AUD 79 (= USD 83) each way.

This could be an inexpensive stopgap that could save you a few Avios, and in fact at those fare levels it might even not be worthwhile redeeming Avios at all in any event.