Several online brokers have charges around $20 per trade (e.g. Commsuc, Macquarie Prime), and there may be a few cheaper as asteroider has posted (e.g. belldirect).
More important thing is to find one that works RELIABLY. You could be looking at a difference of $5-10/trade between something that still works when the markets are flying/tanking, and something that leaves you high and dry, frantically trying to contact your broker by phone !
With potential losses of thousands of dollars when your online broker falls over at critical times, I'd say the variations in broking COSTS are insignificant. I'm currently with Commsuc, but considering a move to Macquarie Prime (same brokerage cost) for improved RELIABILITY.
