The scheme, which covers a wide range of product categories, is currently being tested in 23 company-owned stores.
Dedicated pos material has been designed, and work is under way to create a rolling stock cycle to keep the offer fresh and exciting for shoppers.
Costcutter trading manager Adam Walker said the company would be monitoring the results closely, with a view to rolling the scheme out nationally.
"Here at Costcutter we have a long and recognised tradition of successful promotional initiatives and we're always looking for ways to help retailers maximise sales and profits," he said.
l For more on the rise of the £1 promotion, see p22