No US garrett dealers on ebay will sell a detector to Australian residents due to Garrett's policies, so you will find that the listing will state international shipping, bit when you go to checkout, they will most likely deny the transaction.
Even better value, check the forum for sales section, where Paul_mac 1 has an Ace 350 for sale at $300 which represents great value. The detector looks in great condition, and includes headphones and control box cover. Very good value considering they cost over $500 to buy here (in the guise of a Garrett Euroace).
Buy a new Ace 250 in Australia, and you are looking at around $400 including postage.
Also have a serious look at the Tesoro Compadre for a good quality first detector with lifetime warranty, at around $220 brand new in Australia with an 8" coil.