Pretty much all there in the title. Online ticket sales will close off on 28 August.
That doesn't mean you can't get a ticket to the rally after the 28th, it just means you will need to buy one at the gate and the price will be $70 instead of $60.
Just think what you could do with that extra tenner!
Personally, I'd waste it on food and grog but why not tell us what you'd waste it on in the comments? Best answer earns a prize ;-)