Karen Pryor Clickertraining | dog training and cat training info, books, videos, events -- $1.79 for clicker, $3.45 for shipping to Australia, for a grand total of $5.24. (I think that's AUD$6.04?)
Anywho, I got mine at a petstore. I'm sure you could find one there (or maybe somewhere cheaper online). They're usually in the section with the dog stuff or with the cashiers since they're small.
Some people use a ballpoint pen or click their tongues. There's also a good clicker training group on Yahoo or ask jenseits some questions. She's got her sun conure doing all kinds of cute stuff. :)