With punning allusion to the high cost of living in that affluent harbourside eastern suburb of Sydney, New South Wales, Double Bay is colloquially referred to as Double Pay (also double pay)—as explained in The Sun-Herald (Sydney, New South Wales) of Sunday 13^th August 1978 by Alan Dearn, the Melbourne Herald’s representative in Sydney:

Sydney retailers mark up prices double to what they would dare in Melbourne. The wealthier the suburb the higher the prices. Double Bay, for instance, is known locally as double pay.

These are the earliest occurrences of Double Pay, double pay, that I have found, in chronological order:

1-: From the Tribune (Sydney, New South Wales) of Wednesday 9^th March 1966:

Double pay in Double Bay

Sydney: In Double Bay shopping centre on Saturday morning 91 signatures were obtained to the Labor Council of NSW Prices Petition, in 1¾ hours.
One woman, when asked to sign the petition, said . . . “yes, it is about time something like this was done, they call this place ‘Double Pay’, everything is dearer here than anywhere else, food is dear enough without adding prices on.”
[…]
People of lower and higher income brackets agreed it was time something was done about controlling the spate of price rises over recent months, and in particular since decimal currency introduction.
[…]
Footnote: Tribune’s local correspondent adds: “While some locals call this area “Double-Pay” . . . I would call it “Trouble Bay” for there sure is trouble brewing for someone . . . the locals are pretty steamed up with exorbitant prices, the monopoly grip of Woolworth’s store and the moving in of G. J. Coles who staked a claim in Knox Street on an area where homes once existed—“Trouble Bay” has a few Trouble-Shooters in it now.”

2-: From The Sydney Morning Herald (Sydney, New South Wales) of Thursday 14^th November 1968:

“Double Bay may mean double pay, but the quality is there, and that’s of prime importance to shoppers.”
Real estate agent Mr Doug White, who has had his office at Double Bay since 1963, is most enthusiastic about the area and its potential.
“Double Bay has emerged as a world-renowned fashion centre where wealthy buyers from all over assemble for the finest in fashion and specialities,” he said.

3-: From The Sydney Morning Herald (Sydney, New South Wales) of Thursday 6^th November 1969:

When you think of fashion . . .
By Elizabeth Hawkes

Think of fashion, think of Double Bay, for the two are synonymous.
In no other area of Sydney are so many haute couture houses and boutiques clustered with such concentration, providing fashion in endless variety for everyone from the well-to-do to the working girl.
It can be cheerily friendly or frightfully snobbish.
It can be a case of “double pay”—or of getting the best of quality and value too.

4-: From The whole world comes to Double Bay, by Lenore Nicklin, published in The Sydney Morning Herald (Sydney, New South Wales) of Saturday 15^th May 1976:

Double Bay is the best shopping centre in Australia. For Perigord truffles, or pillowslips, or $300 suede shirts, or avocado pears, or Chloe dresses, or French knickers, or Swan beer, or Polish salami. It is gay, glamorous, full of life. It is also tough, seedy, and fiercely competitive; hustler-territory. It is smoked glass and stainless steel—and shoebox architecture, liver-coloured bricks and bloomers hanging on a line in an upstairs balcony.
The Mercedes cars may all be on hire-purchase, but there’s a smell of too much money, a whiff of corruption. “I knew Sydney had finally arrived as one of the big international cities of the world when gigolos began to appear in Knox Street,” said an Eastern Suburbs matron. Melbourne’s Toorak Road territory is tame by comparison—and boringly Anglo-Saxon compared with the rich cosmopolitanism of “The Bay.”
“Why does everyone send up Double Bay?” asked Tony Yeldham of the Squire Shop. “What about the basic people?” He was sitting on the floor of his shop going through boxes of men’s swimming trunks in search of a certain size. (Outside, some of the basic people emerged from a particularly large Rolls-Royce, and an Airedale walked past—Afghan hounds do seem to be thinner on the ground this year.)
“And why does everyone say Double Pay,” continued Mr Yeldham. “We all know it’s expensive.”

5-: From The Sun-Herald (Sydney, New South Wales) of Sunday 2^nd April 1978:

$450 a week at Double Bay not even top rent

While flat-seekers are wearing out their shoe leather in the Northern and Western suburbs, a well-heeled Double Bay resident this week offered to rent his luxury house for $450 a week.
As they say in the East, Double Bay really does mean Double Pay.

6-: From this advertisement, published in The Sydney Morning Herald (Sydney, New South Wales) of Wednesday 9^th August 1978:

Lifestyle is Sydney’s only specialist shop for Continental Quilts pillows and bed linen.
Save now on famous Lifestyle Continental Quilts for the deepest most luxurious natural sleep money can buy.
Come in and see Linda Prowse at 375 New South Head Road, Double Bay, (just because we’re at Double Bay, doesn’t mean we’re double pay).
Quality at prices you can afford.

The reference to Double Bay is implicit in the following from Column 8, published in The Sydney Morning Herald (Sydney, New South Wales) of Friday 20^th February 1981:

They’re selling that Australian institution, Throaties, at the Opera House. Smart idea—anything that stops the Concert Hall reverberating with coughs during a performance of Otello is welcome. The Throaties, however, are being sold at 50 per cent above the recommended retail price. This may seem a small point, but it’s yet another irritating example of Opera House tenants’ unswerving devotion to Le Rippe Off, on the assumption that everybody who goes to the place is from Double Pay.