We just started 6 month rego's in NSW & when I looked into it, it costs exactly the same. I thought it'd be more for 6 months, but the costs were exactly halved, so come the full year, it was exactly the same price in total. (Exaclty, lol. Sorry)
Must be different in QLD. For a 6 cylinder car in early June it was $369 for 6 months or $706.35 for 12 months. CTP insurance was included in those amounts at $171 or $326