Just wanted to start a guide on keyboards which are listed on eBay.
I work for the retail store 'haworthguitars' and have been stocking Casio and Yamaha keyboards for over 5 years now.
Casios keyboards come with a 3 year warranty and Yamaha with a 5 year. Even if you purchase from the other side of the country there will probably be a local service centre who can help you out if you have any problems.
Please, please, please do not buy anything from overseas - firstly the standard power supply will not work with Aussie voltage, secondly what would you do if the keyboard was faulty?
Stick with the brand names and you will get a great keyboard which will last you for years and years.