Honestly as a British expat in Australia I really really hate this show!
Lots of reasons, but I can't elaborate on them all as I don't have time but a few things...
"Oh I couldn't leave my family
"
"We'll be 7k GBP a year better off! Omg lets go!" 
Or "oh my god everything's so expensive" etc etc. on average, yes. And I believe that's due to higher "average" prices.
So if you have say, 1 value chicken, 4-5 midrange and 20 organic premium dipped in gold would feed 17 for a week chickens, on average sure they'll be more expensive and I think that's what makes it more expensive, as here there tends to be more premium/better quality options vs supermarket own brands.
The best way is to (if in Aus) get out there and look, do a shop or even just a meal plan/list!
If not, use a dummy address to create a Woolworths grocery account, get on there and do a fake weekly or monthly shop.
Another thing that makes me
is when the family are renters and proposing a move to qld, council tax/council rates are often still compared. In Queensland a renter cannot be made liable for council tax and it's very very expensive/difficult (due to the fact that renovations and water efficiency measures much take place first) for renters to be made liable for water rates too.
A lot of properties don't have any gas whatsoever either.
Also it's clear that the couples/families are on holiday rather than actually getting a feel for what it's like to be there, which you can only really do by coming over for a couple of months, living in a short term rental, not eating out or spending every second at the beach and talking to prospective employers, talking with migration agents about a visa you can live there on etc etc rather than oooh Australia is sunny put a shrimp on the barbie!!!