ERP Implementations are complex! So many moving variables among which key decisions are to be made. One of the challenges is to get good visibility on breakdown structure of Total Cost of Ownership (TCO). Following diagram will help you. You can use this during various stages of the project (Initiations/discovery – developing business case, Vendor Selection, Implementation etc.). All the cost elements may not be applicable to you. For example, if you choose to implement SaaS offering, Hardware elements are not applicable to you. Trust you will find this breakdown structure helpful!