Generally you need to start with an overseas validation through CASA. (Address is 39 Navigator Place, Hendra, Brisbane).
As for private hire, QLD Aviation Services at Caloundra (07 54927040) does PA-28/C172 around the $170 Mark, PA-34 at around $340 (inc GST). Tends to be a little cheaper than GAAP or CTA aerodromes due to a lack of landing fees and charges.