We introduce a quantitative concept for bisimulations by integrating the notion of amortisation (cf. [3]). This allows us to make behavioural comparisons between nondeterministic systems that are inherently non-terminating and to analyse the relative long-term costs of deploying them. To this end, we conservatively extend CCS to include a new set of cost-based actions and define a cost-based quantitative relation called amortised bisimulation. We demonstrate the applicability of our approach by two case studies. In both cases the cost of additional administration is shown to amortise. We furthermore show that the amortised preorder for speed introduced in [6] is naturally expressible in our setting.