Starting with something small is an excellent idea! I have seen too many beginners just plain quilt because the quilt they started was the size of Egypt!
I don't know anything about the cost of fabric or batting in Australia, but I can tell you how long it usually takes me to make a quilt. I know because so many people asked me that I finally just timed myself through sort of an average quit, which in my case, would be twin sized. ..40 hours. I quilt on my machine and that is part of my figuring.
I am still a bit of a beginner, so I don't pick really complicated patterns. I didn't count picking out my pattern or fabric as part of the 40 hours, though does40 hours does include cutting the fabric.
Hope this is helpful?
This is a great hobby. I hope you enjoy it. I swore I would never quilt, and am on quilt 26. (I started attending quilt meetings 2 years ago, just to keep my sister company and got hooked.)