On course bookmakers can only accept phone bets of $150+ in Victoria and higher in NSW - not sure about QLD. The Vics are coming down to $50 within a couple of years.
The 5% take on top fluctuation bets by Mark Read's organisation is a rip-off and has to be avoided. There is another crowd that are based in NT that used to be in Vanuatu - they used to be called Number One betting shop but have now changed to something else - a good net search ought to find them. They will give you top fluctuation without taking a slice on a $50 minimum wager.