The focus is on the outsourcing of services from the public sector to the private sector. Our model compares the possible price advantage with the transaction costs. The project focuses on measuring the course of transaction costs and quantitatively determining the (maximum possible) level of these costs. For this purpose, the risk perception of the decision-makers is measured at different degrees of spin-off. Since the services can be very specific, it can come to the situation that exactly one buyer meets exactly one supplier. For this bilateral monopoly, it is necessary to determine determinants that make it possible to determine the equilibrium quantity and price. In addition, the model is used to give recommendations for action on how to structure the cooperation, depending on the specificity, the degree of outsourcing and the course of transaction costs.