good ol' ebay has a few different ones that claim to be "tailer made" for individual cars, even if you didnt want those particular ones, it gives you an idea of cost.
It cost bout 250 for a rear seat n bout 100ea for the front from like autobarn n place like that...
Bit exy i recon but they do look sweet as they sit perfectly on the seats tho...
If your car has side airbags a standard seat cover is not compatible as it will interfere with the air bags if and when they deploy.
Holden have what they call car seat inserts for cars with side airbags.