A developing emphasis of health care reforms has been creating organisations with responsibilities for strategic commissioning of services for defined populations. Such organisations must set priorities in aiming to meet their populations' needs subject to a budget constraint. This requires estimates of the health benefits and costs of different interventions for their populations. This paper outlines a framework that does this and shows how this requires modelling to produce estimates in a way that is transparent to commissioners, of requisite complexity to produce sound estimates for priority setting using routinely available data. The example illustrated in this paper is an intervention that would improve glucose control in the English population with type 1 diabetes. It takes many years for a change in glucose management to deliver maximum benefits; hence the intervention is not good value-for-money in the short run. We aim to give a more strategic view of the costs and benefits modelling costs and benefits in a steady-state model which suggests that the intervention is good value-for-money in the long run.