Make an offer to the seller that you’ll do cosmetic cleanup work on the house in exchange for the deposit or downpayment, i.e general cleaning, painting, landscaping, etc. Sometimes it works!
Really, though…a deposit would probably be seen as an indication of one’s good faith in completing the transaction - hence the “earnest money deposit” as it is referred to in America.
Don’t know about Oz but a deposit isn’t necessary to bind a deal, just “consideration”.
So whatever the Seller is willing to accept should be good enough. Use some creativity and you’ll figure something out.