Prices have been locked at $2 for Countdown's Select brand 200g chocolate biscuit range since October 2013.
Griffin's Squiggles and Chocolate Fingers were on sale for $2.49 last week for a 200g packet at Countdown against a usual price of $3 or more.
Griffin's has been regularly cutting the prices of favourites such as Toffee Pops and Mallow Puffs.
Sales of chocolate biscuits last year were up 15 per cent on 2013 - but the money we spent jumped by less than 9 per cent.
Nielsen client service senior manager Priyanka Manchanda said fierce competition was behind the difference. That would continue as long as prices stayed low.
"It's definitely become more competitive."
Statistics NZ said surveys showed the average price of chocolate biscuits in December 2011 was $3.10. Last December it was $2.99.
Professor Cliona Ni Mhurchu, who works at the National Institute for Health Innovations at Auckland University, said consumers were driven to look for bargains and to feel bad if they didn't make the most of them.
Biscuit makers banked on people buying more when prices went down, she said.
"It's working [for them] and it works for consumers because it makes shopping cheaper."
Griffin's wouldn't comment but Countdown merchandise manager Steve Mills said the chain had noticed increased demand.
"[That's] partly due to some great prices, but also because the growth statistics reflect the slower year before."
Foodstuffs declined to comment.
Australian giant Arnott's - which makes biscuits such as Tim Tams and Mint Slices - imports its biscuits and has so far resisted large price cuts.
Nielsen figures show more than 34.5 million packets were sold at Kiwi supermarkets in the year to November 30, almost eight packets for every person.
The value of those sales rose 8.8 per cent to more than $83 million last year. Total biscuit sales rose by 3.2 per cent to about 150 million packets last year.