Maarten,
The retail maps for the Garmin cost dollars because there is an investment in the mapping that requires a financial return by it's legal owners. I'm sure that the cost can be circumvented by downloading the maps via torrent, but rather than tread on the edge of legality, can I offer you some alternatives that will provide quite good mapping at little or no cost that is still legal and within copyright restrictions to load on you GPS?
Shonkymaps Geoscience Australia 1:250k map converted to Garmin format by a dedicated member of the public.
Contours Australia 5m Contour map overlay for your Garmin, generated from the SRTM (US Shuttle collected data) by another dedicated member of the public.
Open Street Map Australia OpenStreetMap road and trail mapping for your Garmin, collected by hundreds of amateur mappers and the Garmin conversion performed by yet another dedicated member of the public.
Once you are familiar with these maps you may well find that they suit your needs and in some cases outperform the commercial offerings. I have a VistaHCX myself and have never used any mapping but these on it, with great results.