The cost of living is increasing. So what's behind it?

Fancy a cheaper barbecue, dining table or building supplies? The secret might be to go shopping in Australia.

Shoppers were angry last week when it was revealed that a garage door emergency access lock from Bunnings was selling for less than A$20 ($21.30) in Australia but more than $50 here.

It's far from the only example.

Within Bunnings, building products such as fascia board were another category were Australians got a better price - up to 50 per cent or more off, in some cases.

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But other retailers are at it, too.

Mitre 10 has a Weber Family barbecue for A$759.00 ($808) in Australia - in New Zealand this retails for $959.

An Arco dining table from Freedom Furniture is A$799 in Australia and $999 here.

In Australia, Michael Hill is advertising a men's chronograph watch in blue and rose tone stainless steel for A$299. Here the same watch is $349.

123RF New Zealand retail is a smaller market, which can mean higher prices.

At JB Hi-Fi a video doorbell is A$328 in Australia and $379 here.

Jacqui Coombes, Bunnings director of New Zealand and group human resources, said the individual size of the markets, freight and shipping, as well as differences of suppliers, could cause a disparity in price between items stocked in New Zealand and Australia.

"We always aim to provide great value for our customers wherever they're shopping. This includes sourcing from local suppliers, regularly checking competitor prices and maintaining our commitment to lowest prices. As always, if customers find a New Zealand competitor's lower price on the same stocked item, we'll beat it by 15 per cent."

A spokesperson for Freedom Furniture said the New Zealand company and Freedom Furniture Australia were separate companies, which bought different volumes and often different ranges entirely, so factors including the exchange rate, differing GST and freight variances played a part in local pricing.

At Michael Hill, a spokesman blamed similar factors: exchange rates, GST, import duties and distribution and freight costs.

"These economic factors are common practice and apply to all international brands operating in multiple markets."

He said Michael Hill had operational measures to ensure value for customers was maximised in a sustainable way.

SCREENSHOT Australian shoppers get a better deal on this doorbell.

Greg Harford, Retail NZ spokesman, said prices reflected a range of costs, and there was variability between Australia and New Zealand.

"Businesses do not necessarily have the same operating model on both sides of the Tasman, and the small scale of the New Zealand market can drive cost differences.

"There could be marketing factors at play - something might be on special in one market but not the other - and there may be less customer demand in New Zealand which can drive up unit costs.

"Depending on the distribution model, there could be higher transport and logistics costs for servicing New Zealand. This is true domestically as well as trans-Tasman. Some goods can be more expensive in Queenstown than in Auckland."

Taxes and tariffs also make a difference. There is no GST on fresh vegetables in Australia but we pay 15 per cent on everything.

SCREENSHOT Michael Hill sells this watch cheaper in Australia.

He said people should take a long-term, holistic view of the market.

John Tookey, head of department in the Built Environment School of Engineering, Computer and Mathematical Sciences at AUT, said there were issues of scale.

Retailers in Australia were able to easily access much larger numbers of people across smaller geographical areas - Sydney has the same population as New Zealand. The cost of catering for that market in one city was much less than trying to service shops from Invercargill to Kaitaia with the same potential turnover, he said.

"Our overheads are very high here because there's a small market spread over a huge area."

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