Two points in response, 1: Australian opal is not found deeper than Ethiopian and therefore contains more water. Welo (Ethiopian) opal is located literally multiple hundreds of feet below the plateau, almost all volcanic opal that is non- hydrophane is extremely unstabe and will crack quickly (All commercial Ethiopian opal is porous hydrophane).
The deepest Australian opal has historically been about 120 feet but the average is about 30-50 feet in depth continentally, and the retention of water in the structure is due to the ‘quality’ of host rock weathering and resulting residual mineral salts infused in the material. Generally the more pure (well filtered) the host rock and opal is the more long term stability regardless of water content.
2: The price point of Australian opal is arguably justified as a large proportion from high quality fields such as Andamooka, Old Lightning Ridge nobbies, Coober Pedy’s Olympic, 7,8,9,10, 23 Mile, Opal Valley, Allans Rise, Opal Ridge etc, much of White Cliffs and Mintabie produced gems that are practicably glass, meaning they are non hydrophane, super stable heirloom quality gems that will not absorb water, oils, perfume or soaps etc, will not craze or crack naturally, thereby making them an objectively superior gemstone.
I have also read elsewhere that the Australian opal market is ‘controlled’. I don’t see how this is possible with thousands of small companies and operators finding small to large parcels and selling in many different ways and on many different platforms. It is actually one of the most freely unregulated markets on earth!