Coincidentally, in the last couple of weeks three people have asked me about buying an SLR camera. Taking up photography as a serious hobby can cost quite a bit. It is good to put the various costs into perspective so that one can see the whole journey ahead before taking a shot at it (pun intended)
Buying the SLR is just the first in a series of purchases you are going to make. But hang on; don't go buying everything until you grow into it. You'll appreciate it more when you acquire the pieces carefully and with great discernment over time.
First, the lens. You probably will start off with the kit lens, which is good. I have a zoom kit lens (18-105mm) which I use almost all the time and I still find it adequate for almost all my needs. Over time, when you find yourself venturing into different genre you will find it useful to buy just what you need. There are lenses to suit closeups, portraits, landscape, sports, and wildlife - to name the common ones.
You will need the basic accessories: a proper camera bag, an extra battery, a large memory card. These things will last you years, so get good ones. A good camera bag cushions your camera and lenses. An original battery is more dependable than third party ones. A good quality memory card ensures you don't lose your images. Conservatively, these could set you back about AUD$250 in total.
Every serious photographer needs a tripod. A good basic one costs about $300 (Manfrotto 190XPROB, with head and adapter).
You will learn to appreciate the use of a polarizer and perhaps other filters. These can be added to your gear over time. A flash gun will be useful too, when you need to take photographs at a function. A good flash gun is worth investing in, as it can last you over the lifespan of many cameras. A top of the line one costs about AUD$650-$850.
At this time, I would assume you already have a suitable computer with adequate hard-disk space and processing power for image editing.