With the evolution of cloud computing, the efficiency in terms of the cost of cloud services has become a significant concern. One way of obtaining efficient costs of cloud services can be by comparing cost estimates of specific cloud services across different cloud service providers. Then again, comparing cost estimates can get complex and challenging. A number of factors contribute to the complexity, including the high number of cloud service providers, the quest to locate the cost estimation tools provided by these providers, the process to familiarize oneself with the complexity of these tools, and a host of other considerations. In order to address these issues, this research proposes and explores different software architecture approaches to build a software application that provides cloud service comparisons across various cloud service providers. Two main aspects of cloud computing cost estimate comparison are cloud service providers and cloud services. Considering the two aspects, we proposed software architecture approaches that support extendibility in terms of cloud service providers and cloud services. Additionally, this research includes comparisons between different software architecture approaches that we proposed, arguing which approach is best suitable with respect to extendibility in terms of cloud services and cloud service providers. Moreover, as a prototype, an angular web application is built based on the most suitable software architecture. The objective of this research is to provide conceptual and practical aid to developers who want to develop extendible software applications that provide cloud service cost estimation comparisons across different cloud service providers.