Cloud computing brings many benefits to the enterprises who decide to migrate their applications to the Cloud partially or completely. This thesis focuses on helping users finding the most cost-efficient between different Cloud offerings which have similar features. Data from several Cloud providers are collected and organized in order to implement a Cloud provider knowledge base exposed as a set of web services. These services are validated against other similar systems and exposed as RESTful APIs. A decision support system is built in this work based on these APIs and evaluated by an existing use case with different migration plans.