Hi Becky....I can remember being your son's age and having a very keen interest in astronomy, I was somewhat younger than he is now, when I first started, but even so if you can really encourage him, he'll have a lifelong hobby. Who knows, he might even become an astronomer when he grows up
So far as telescopes go, in your price range ($250-$300), one of the smaller Celestron or Skywatcher refractors would be an excellent choice of scope. You may be able to pick up one from one of the larger camera shops, as they do stock these telescopes, however, if you can't get them there (I'm assuming you live in Perth), have a look at these sites...
Bintel
MyAstroshop
Andrews Communications
They have a few good scopes in the price range you're looking at and if you need to have it shipped, they will help you with this as well.
Good luck with your telescope hunt and I hope your son really gets into astronomy. It's a great hobby and a wonderful subject to be interested in