The only skylight I would consider is from Velux as they have double glazed units with lots of shading and openable options. I would steer well clear of the old fashioned polycarbonate dome type as you have no control of the heat gain (or loss). Cost depend on size, slope of roof, type of roof construction, block-out screen and openable options. With the screen and openable options you also have the option of powering it through your homes electricity, in which case you will need a powerpoint installed in your roof space, or using integrated solar panels and battery.
There are lots of Brisbane based companies that do supply and install for Velux skylights, so they should be able to quote.
Bunnings also sell them if you check out their website, but you will need to arrange installation yourself, and in my experience it is better to go through a supply and install company for a better guarantee against potential roof leakage problems.
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