One measure of organizations' performance is the cost of products, as this may indicate the level of efficiency and contribute to define the business strategy of the firm. Nevertheless, companies face an increasingly fast-changing environment where the variability in processes, products, technology, prices, among other variables affect the performance of the organization. Particularly, given such changing environment, product and service costs may be changing over time. In this context, deterministic models for costing systems might be inappropriate. Thus, this chapter proposes a model for calculating costs which considers the variability of endogenous and exogenous cost variables. It uses the logic of a Two-Stage costing model and Monte Carlo Simulation. The proposed model may allow to some extent to predict the risk associated with the variability in costs and support the necessary steps which should be taken to better manage such risk, whether from the point of view of processes rationalization and of cost management.