Malcolm,
I know you're on a tight budget but there are a couple of good suppliers of CNC components in Oz.
Ausx
Homann Design
I'm a happy customer of both.
A suitable stepper for your design will set you back about $45 - $50.
If you're into woodworking, there's a local woodworkers forum that has a great CNC section.
http://woodworkforums.com
Look forward to seeing the rest of your build.