Due to multiple factors, expect to potentially pay more when booking in December. For low rates, February can be a great choice for travel to Perth. Flights to Perth from Tempe in February are about $1,459 on average during February, but can be found for as low as $1,033.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Tempe to Perth as you normally would.