It varies a bit - as does the quality of planes and the 'service'. Try googling around but some places won't even advertise their prices. It's become much more expensive here in recent years with fuel price increases and more 'user overpays' policies - especially at capital city GA airports which are becoming very expensive now. One wonders how they stay in business as their returns disappear as their prices go up and more and more folks walk away. Nice quiet places fly these days though :-)
Here's one to get you started, probably near the top of the pile as they go..
Aircraft Hire - Cessna, Piper, Beechcraft, Pitts and more - Sydney, Australia