I went through all the grabaseat deal dates to Australia, and just searched for the best return flights I could find. There may well be cheaper, but this was ~13,000 searches running overnight, so it's a fairly good indication.
Some are Jetstar, some Emirates, some connect to a Virgin Australia flight, but you can always use the filters to specify the one you prefer.
Summary:
Auckland to Adelaide return (27 Jul 25 - 30 Aug 25) from $691 return
Auckland to Brisbane return (20 Jul 25 - 30 Aug 25) from $391 return
Auckland to Cairns return (26 Jun 25 - 13 Aug 25) from $627 return
Auckland to Gold Coast return (15 Jul 25 - 26 Aug 25) from $392 return
Auckland to Melbourne (Tullamarine) return (1 Jul 25 - 12 Aug 25) from $439 return
Auckland to Perth return (1 Jul 25 - 2 Sep 25) from $920 return
Auckland to Sunshine Coast return (26 Jun 25 - 8 Aug 25) from $378 return
Auckland to Sydney return (7 Jul 25 - 31 Jul 25) from $458 return
Christchurch to Adelaide return (27 Oct 25 - 24 Mar 25) from $747 return
Christchurch to Brisbane return (24 Jul 25 - 29 Aug 25) from $608 return
Christchurch to Cairns return (26 Jun 25 - 12 Sep 25) from $482 return
Christchurch to Gold Coast return (27 Jul 25 - 25 Aug 25) from $438 return
Christchurch to Melbourne (Tullamarine) return (1 Jul 25 - 29 Aug 25) from $513 return
Christchurch to Sunshine Coast return (25 Jul 25 - 16 Sep 25) from $577 return
Christchurch to Sydney return (1 Jul 25 - 30 Jul 25) from $606 return
Dunedin to Adelaide return (26 Jun 25 - 20 Aug 25) from $827 return
Dunedin to Brisbane return (20 Jul 25 - 29 Aug 25) from $614 return
Dunedin to Gold Coast return (15 Jul 25 - 28 Aug 25) from $400 return
Dunedin to Melbourne (Tullamarine) return (1 Jul 25 - 16 Aug 25) from $698 return
Dunedin to Perth return (26 Jun 25 - 13 Sep 25) from $1085 return
Dunedin to Sydney return (7 Jul 25 - 31 Jul 25) from $584 return
Napier to Brisbane return (20 Jul 25 - 31 Aug 25) from $620 return
Napier to Gold Coast return (15 Jul 25 - 27 Aug 25) from $581 return
Napier to Melbourne (Tullamarine) return (1 Jul 25 - 17 Aug 25) from $678 return
Napier to Perth return (29 Jun 25 - 19 Aug 25) from $1270 return
Napier to Sydney return (7 Jul 25 - 31 Jul 25) from $750 return
Nelson to Adelaide return (26 Jun 25 - 20 Aug 25) from $1049 return
Nelson to Brisbane return (20 Jul 25 - 31 Aug 25) from $708 return
Nelson to Gold Coast return (15 Jul 25 - 27 Aug 25) from $573 return
Nelson to Melbourne (Tullamarine) return (1 Jul 25 - 17 Aug 25) from $757 return return
Nelson to Perth return (29 Jun 25 - 26 Aug 25) from $1317 return
Nelson to Sydney return (7 Jul 25 - 31 Jul 25) from $799 return
New Plymouth to Adelaide return (26 Jun 25 - 13 Aug 25) from $1021 return
New Plymouth to Brisbane return (20 Jul 25 - 29 Aug 25) from $592 return
New Plymouth to Gold Coast return (15 Jul 25 - 27 Aug 25) from $581 return
New Plymouth to Melbourne (Tullamarine) return (1 Jul 25 - 13 Aug 25) from $662 return
New Plymouth to Perth return (2 Jul 25 - 18 Sep 25) from $1283 return
New Plymouth to Sydney return (7 Jul 25 - 31 Jul 25) from $718 return
Palmerston North to Adelaide return (26 Jun 25 - 26 Aug 25) from $1041 return
Palmerston North to Brisbane return (20 Jul 25 - 28 Aug 25) from $604 return
Palmerston North to Gold Coast return (15 Jul 25 - 27 Aug 25) from $605 return
Palmerston North to Melbourne (Tullamarine) return (1 Jul 25 - 17 Aug 25) from $667 return
Palmerston North to Perth return (30 Jun 25 - 26 Aug 25) from $1289 return
Palmerston North to Sydney return (7 Jul 25 - 31 Jul 25) from $777 return
Queenstown to Brisbane return (26 Jun 25 - 1 Aug 25) from $617 return
Queenstown to Melbourne (Tullamarine) return (26 Jun 25 - 12 Sep 25) from $548 return
Queenstown to Sydney return (26 Jun 25 - 5 Nov 25) from $508 return
Tauranga to Adelaide return (26 Jun 25 - 31 Aug 25) from $1031 return
Tauranga to Brisbane return (20 Jul 25 - 31 Aug 25) from $673 return
Tauranga to Gold Coast return (15 Jul 25 - 27 Aug 25) from $677 return
Tauranga to Melbourne (Tullamarine) return (1 Jul 25 - 17 Aug 25) from $758 return
Tauranga to Perth return (2 Jul 25 - 26 Aug 25) from $1334 return
Tauranga to Sydney return (7 Jul 25 - 31 Jul 25) from $851 return
Wellington to Brisbane return (8 Jul 25 - 28 Aug 25) from $559 return
Wellington to Cairns return (26 Jun 25 - 19 Aug 25) from $658 return
Wellington to Melbourne (Tullamarine) return (1 Jul 25 - 29 Aug 25) from $624 return
Wellington to Sunshine Coast return (25 Jul 25 - 16 Sep 25) from $564 return
Wellington to Sydney return (7 Jul 25 - 31 Jul 25) from $560 return
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Some dates say till 2026. Is this accurate?