How costs are distributed among the participants is a key question in the management and viability of shared resources. Although all cost-sharing mechanisms are subjective and thus it is eventually up to the participants to accept one or another, some general criteria seem desirable, such as being budget-balanced and that, in any case, a participant pays more when not cooperating with anyone else. In this paper, we analyse the cost-sharing mechanism that the Guifi.net community network has developed and put in practice to split the transit costs among their more than 20 participants for almost a decade. Our results show that the Guifi.net’s cost-sharing mechanism of the external connectivity, which comprises an equal membership fee for each participant plus a proportional distribution of the remaining costs according to the resource consumption, yields a cost assignment similar to the Shapley value. Our analysis also shows that any alternative to the coalition of all participants entails significant total cost increases and detrimental widespread cost allocation.