Avoiding the major supermarkets when buying fruit and vegetables can cut your bill, and you don't always have to go out of town to shop, a Herald survey has suggested.

Prices for some of the most common produce in the Foodtown store in Mt Eden were more expensive than the Freshworld located just across the carpark.

But independent retailers are selling produce at prices far above what they would be paying wholesale.

The spot-check supported claims by the Green Party this week that major supermarket chains were ramping up the price of vegetables, selling produce at up to 500 per cent what they paid growers.

From each store, the Herald bought four apples, one avocado, one bunch of bananas, one head of broccoli, a cabbage, two peppers, four carrots, one cucumber, one lettuce, five button mushrooms and four white potatoes.

While there was a small difference, the price variations between Freshworld and Foodtown were not wildly different.

Foodtown was on average 5 per cent more expensive than Freshworld. Five items were more expensive, three cheaper and three the same or within one cent. Both stores sold items well over what they paid to growers.

Using Horticulture New Zealand's estimates of wholesale prices, roughly calculated retailer mark-ups ranged from virtually nothing for white washed potatoes to 458 per cent for iceberg lettuce.

The association's chief executive, Peter Silcock, said retail prices were "out of line".

"The fact is, our growers are struggling to cope with a cost price squeeze that is reducing real returns," Mr Silcock said.

"Growers and consumers alike need to be confident there is enough transparency in the pricing system to ensure a consistent and acceptable mark-up range, rather than the extremes we see now."

He said an independent investigation, perhaps led by Justice Minister Simon Power, could explain where the costs were in the supply chain, and where profits were going.

Foodtown owner Progressive Enterprises' managing director, Peter Smith, said the company's prices were fair. Differences in price often came down to quality, he said.

"There are a number of factors that contribute to price. Quality in particular is a significant factor. If the price is compared on two products purchased at different stores, it is difficult to determine whether they are of the same quality, from a specific region or grower and what quality assurances come with the product."

Food and Grocery Council chief executive Katherine Rich earlier spoke in favour of looking into a supermarket code of conduct to ensure food suppliers were treated fairly, as suggested by the Green Party.

But she yesterday said supermarkets were not ripping off customers and it was not fair to compare the prices growers received with supermarket prices.

"There are a lot of costs that are incurred throughout the supply chain," she said. "A lot of goods get thrown away."