The tourist looking to see “nature” in Australia should be aware that National Parks tend to work in tandem with commercial interests, since the funding by the state and national governments appears to be mostly aimed at providing maintenance (access roads, prescribed burns etc) and trail maintenance and development. We saw very few visitor centers staffed with park personnel that did not have a larger component that was a gift shop or a restaurant of some sort. The natural history displays about the park itself were a minor part of the facility – even where they are noted as being exceptional (as in the Pinnacle Desert Park north of Perth).
Outside of National Parks there may be many attractions, that by reading the description, appear to be associated with the park itself. This is often not the case, and the attraction requires a separate fee for entrance. These can be high when compared with US park entrance fees, though they are perhaps comparable to similar commercial attractions in the US. We rarely visit such attractions in the US since the park systems (national or state) tend to have better preserved examples of what we might be looking for, and the entrance fee is clear. In Australia, most natural attractions (like anywhere else) that are well-advertised are commercial and must cover their advertising cost and make a profit. They tend to do an amazing effort to hide the actual entrance fees in the advertising; this we also noted for many other commercial facilities. Putting the actual price of any service or item “up-front” seems less common in Australia than in the US.
Despite the above comments, the commercial attractions in Australia related to “nature” tend to have spectacular engineering efforts associated with them. A number of the rainforest canopy walks, ocean lookouts, or nature parks with animal displays are “world-class” a term they like to use in Australia. Also many attractions are noted as being as “World Heritage listed” sites. This term, not widely used in the US, refers to a UNESCO designation.
As for National Parks, some states do not require an entry fee while others charge 12 AUD daily. In some parks in Western Australia and elsewhere fee machines have been installed, even taking VISA (see photo on this page). In Western Australia tourists can buy a sticker that permits 4 weeks of unlimited entry into parks for $44 AUD. In other states there may be annual permits, but we found it inconvenient or not possible to get anything other than daily permits for other states. Some states required permanently affixing a sticker to the window, inconvenient for a rental vehicle.
Enforcement of entrance fees was almost non-existent from our observation, but might be more strict for camping permits, which in some states was only done online, or in other states only on-site. In fact, we reserved a camping site in a Queensland national park and when we showed up it was occupied. Fortunately, the other campers readily moved to their assigned site. There is no national standard for either park entrance fees or camping procedures – each state is different.