Background Substandard and falsified medicines (SFMs) are a public health concern of global importance. Postmarket surveillance in the form of medicine sampling and quality testing can prevent and detect SFM, however, there is remarkably scarce evidence about the cost and value for money of these activities: how much do they cost and how effective are they in detecting SFM? Methods Between February and October 2022, Systematic Tracking of At Risk Medicines (STARmeds) collected and analysed for quality 1274 samples of 5 medicines from physical and online retail outlets in 7 Indonesian districts. We collated data on the resources consumed by STARmeds, related to all stages of medicines sampling and quality testing including design, fieldwork and laboratory analysis. We used activity-based costing principles to calculate the financial and economic cost of medicine quality surveillance from the perspective of a hypothetical medicines’ regulator. We calculated the cost per day and per week