Most international visitors who come to Cairns do so to visit the nearby Great Barrier Reef. This city is officially in the Tropics so it’s warm or hot all year round, and the main variable is that summer (December through February) sees higher humidity and much more rainfall than the rest of the year.
The good news for budget travelers is that Cairns tends to be at least a bit less expensive than the large cities in Australia when it comes to hotels and even food prices at casual places. The bad news might be that the diving excursions and other adventure sports that motivate people to come here are all kind of expensive.
Hotels in particular start off at much lower prices than you’d find in the big cities, although in high season you might not think so. Backpacker types can at least find some bargains in Cairns, so lingering here should be cheaper than most other parts of Oz.