As an example... usint ITA looked up SYD-KUL and it reported a flight on 6/dec for $847.
Enter this into austrian web site and it gives me price $609 + $254.76 = $863.76
Enter into zuji - $609 + $254.76 - $12 (discount) = $851.76
Bugger all difference really, but using ITA gives a good ballpark figure.