If you have a credit card attached to your PayPal account, you can use that as a funding source instead of a pre-existing balance or bank account. I believe the link is labeled as "More Funding Options". If it's a foreign currency, you also will then see PayPal's EXACT AUD amount they'll charge you. You can alternatively choose to have eBay pull from the credit card in the sold currency, and then your bank will likely give you a different rate. I believe the link is labeled as "Other Conversion Options".

It's best to KNOW your credit card's foreign currency markup as if it's less than PayPal's 2.5%, you'll tend to do better using the card's conversion, but when you use your credit card, you usually get the currency rate of two days in the future, so try to be aware of trends as best as you can be.