While highly unlikely to apply to this domain, you can sell within the first 6 months if they agree the circumstances warrant it. I didn't know this until recently when I sold a 2 week old .com.au and they agreed to transfer the domain.
You can apply to auDA under special circumstances, however in the case of a domain like ebay.net.au - I don't think 'special circumstances' will apply. The idea behind asking for an exception to the rule is more related to cases where a business owner lost their domain (failed to renew) and the new owner has agreed to transfer the domain back at reasonable cost. Usually cost of acquisition.
auDA don't typically ask questions about the amount, but if the owner complains that you are asking for too much money then they may step and ask more questions or seek proof.
You would normally run this process through the registrar of record. Contact your registrar, inform them of the situation. The registrar will then contact auDA on your behalf and request the exception to the 6-month ruling.
NB: People often go directly to auDA relating to many policy questions. I would recommend always requesting assistance from the registrar first, after all they are more familiar with policy and less likely to make a wrong statement. A good registrar will manage this process for you, and technically - its their job! Something to consider & evaluate when searching for the cheapest registration and renewal prices.
Best Regards,
George