Weka for a start are hugely at risk from both primary and secondary poisoning.
According to statistics - at a 95 confidence interval - aerially applied 1080 is wiping out anywhere between 10 and 50% of weka, tomtit and kea's populations from any given area that's been studied.
Note the word "population", as opposed to "individual". You do realise that individuals make up a population don't you? And so a population of 100 wekas being wiped out at a rate of 25%, means that after a blanket dump, you've wiped out 25 individuals. It's not rocket science
And that's from each aerial dump. Blanket dump that same area in 3 years time (for infinity according to DOCs policy) and be prepared to slowly wipe out weka. And they're just one example
So it's not a matter of what species will be wiped out; it's a matter of when.
As for costings - DoC and AHB spend at least $50m per year on pest control, which if you look at possum numbers currently they're still way up above 50 million individuals, and yet we've successfully managed to blanket dump a toxin into our forests and waterways.
Average price per kg of fur is around $80 / kg (can reach over $100 /kg). In a good season an average trapper can produce 350 kg's of furr, which (at a rate of 15 possums per kg) is 5250 possums.
Employ say 3000 individual trappers across the Nation to look after certain bush blocks, give them a target of 5000 possums each year and pay them a wage, plus a commission of some sort to incentivise it, and you're looking at 3000 ppl x 5000 possums = 15million dead possum's each year.
Which turns into a $80m fur industry (at assumed prices, catch rates, & personal) for instance.
Where there's a will there's a way.
And I don't know the answer for rats