Flights to Cancun, Mexico in January and February 2018.
Not really a route that I've seen go on sale often and ~$100 cheaper than this United deal from 2 years ago.
See link below for sample dates from end of January to end of February 2018.
Flights are with Delta (codeshare Virgin) or United. Stops are in LAX and possibly Mexico City too. Stopovers are good (2-4 hrs) mostly, apart from the return trip to Brisbane at around 10 hours in LA.
Peak season for Mexico at this time of year, temperatures in the 20's and only around 5 days of rain in February. Accommodation may be pricey, but its outside of school holidays and towards the end of the peak season.
This is the email I got from Secret Flying with sample dates.
Just check its not schoolies when you go. I made that mistake. It was pandemonium.