Objective Consumers are increasingly relying on low-cost foods, although it is not clear if the nutritional quality of these foods is fully maintained. The aim of the present work was to analyse the relationship between cost and quality within a given food category. Design and setting The relationship was analysed between nutritional quality and cost for 220 food products belonging to seventeen different categories, controlling for package type and package size. Given that a summary of nutrient information was not available on the product label, a novel ingredient quality score was developed based on listed product ingredients. Results Within a given category, the lowest-priced foods were not different from the equivalent branded products in terms of overall energy or total fat content. Nevertheless, a positive relationship, small but significant, was observed between the price and the ingredient quality score. On average, the branded products cost 2·5 times more than the low-cost products, for an equivalent energy and lipid content, and had a slightly higher (1·3 times) ingredient quality score. Conclusions More studies are necessary to evaluate the nutritional quality of low-cost foods. This evaluation would be facilitated if nutrition labelling was mandatory. Yet in view of the present results, it does not seem to be justified to divert consumers, especially the poorest, from low-cost foods because this may have an adverse effect on the nutritional quality of their diet, by reducing further the fraction of their food budget spent on fresh fruit and vegetables.