Use the Australia Post calculator, remember to clearly state and custom, taxes or any unforseen costs are to be paid by the buyer not the seller and add extra on top to cover the cost of your postage fees charged by eBay. Also ask the buyer if it is to go by air or sea, diffrence in price and time and i cant stress this eneogh, once paperwork has been attached at Australia Post take a quick photo of it in case it does not arrive as proof of shipping and address that it was sent to, good luck  🙂