This document outlines a method for estimating the IT costs of research data management systems over 10 years. It describes costing two types of systems: an externally hosted cloud-based system (Amazon Web Services) and an internally hosted open source system. Key factors that are costed include storage, hardware, software, staffing, and annual inflation. The document also notes some limitations, such as development costs being excluded and cloud pricing changing over time. An accompanying Excel spreadsheet model allows entering storage and other variables to calculate total costs for each system.