Hi Leon,
I had a similar query when I came over about 21 months ago and was initially offered the dollar equivalent of my UK salary (i.e. $1.6 dollars for each pound in my UK salary at the time).
Having done a fair bit of research (I'm an accountant...zzzZZZ) the most significant factor was that the exchange rate had been around $2.2/£1 or better for many years beforehand and although the value of the pound had fallen, local prices hadn't so I went back and asked for a dollar salary of 2.2 times my UK salary - and got it.
I also asked for an addditional $10,000 for schooling as foreign nationals in the ACT are required to pay 100% of the nominal cost of educating their children unless this is waived under their visa terms (it was 30% in NSW and 0% everywhere else) - and got that too.
With $80,000 you could live reasonably well. $80k isabout the salary of the most numerous grade of civil servant in Canberra, and civil servant is the most numerous occupation, so it's probably about median for the city, but a great many families in Canberra have double incomes which would mean you'd see a great many others around you living more comfortably. Nonetheless Canberra is a place where there are no real poor areas; pretty much every part of the city is pretty decent as salaries are on average the highest in Australia and the Federal capital is maintained as something of a show piece.
Of course it all depends what you do with your time and money. Having been here long enough to have done all the museums and found out that there really aren't many places worth visiting in less than hour's drive we're discovering that most people just enjoy the fantastic countryside. The best days to be had are undoubtedly there for the price of three bikes, a bike rack and an 'Eski' (cold box) full of sausages and drinks - you don't even need a BBQ as free gas BBQ's are provided all over the place.
Shout if you need more.