Rio de Janeiro: Australia's underwhelming performance in Brazil is set to come at a cost of as much as $11 million per medal to the taxpayer.

Sailor Tom Burton on Tuesday ended a three-day wait for the country's seventh gold medal of these Olympics when he won the men's laser competition on Guanabara Bay but there was more despair for team sports as the women's basketballers, the Opals, made a shock exit at the quarter-final stage at the hands of Serbia.

Midway through the second week here Australia's overall medal tally remains well short of the official projection, including 13 gold, made by the Australian Olympic Committee last December, and in danger of falling short of the 35 collected in London, which was the nation's lowest at a summer Games since Seoul in 1988.

Australia still has genuine gold medal chances to come in the 50km walk, the men's and women's BMX and in canoeing and kayaking and other medal prospects in sailing, men's basketball, athletics and diving.