Their reasons are justified. they want to make sure that our country is untouched - like its clean green image.
IF someone wants to import live animals, you gots to pay for it.
Discus wholesale for about $4 in South America. Then the importers buy them off the harvesters, and/or the breeders, and bring them here (that is the shortest possible chain - in reality the supply chain is longer). The retail here for about $150.
The parity in price is not all a retail mark up - but is fairly indicative of the costs of quarantine - and that is after realising economies of scale and importing literally thousands of fish in a single shipment. It can take several years to recoup the intital costs associated.
lets assume, they do make it to your door step, which they will not. MAf would then pay you a visit, fine you for intentionally bypassing the system and confiscate and destroy the organisms. And that's just the start of it.