Cahill publicised the prize - which includes a visit to his private box at English Premier League club Everton - after scoring the second of his two goals in Australia's 4-0 Asian Cup victory over India on Monday by gesturing to make a phone call.
Nine people have died and 66 were missing after flash floods swept through the north-eastern Australian state on Monday, following earlier floods which have devasted the region.
Cahill explained afterwards the gesture was to bring attention to the prize he was offering in a charity drive for the victims of the floods.
"I've donated a prize to a telethon and the link is on eBay where two people from anywhere in the world get to bid for a chance to come to Everton and sit in my box to watch a game, have some dinner, watch a training session and get a signed pair of boots and jersey," said the 31-year-old.
"It's something that I thought up with some of the media I was working with to do something special for the cause. I showed the gesture because I want people to call in on the telethon, donate money and bid on my auction.
"This is football but there's a lot more that's going on in the world, and to help people and families that are struggling is my way of showing that I care.
The highest bidder had approached $14,000 early on Tuesday morning, but that figure was expected to climb much higher.
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