The Power BI Desktop is a free download and you can register for the Power BI Service at no cost (with a business email address). This enables anyone to easily start building reports. The Power BI Service becomes a paid requirement when you wish to share and distribute reports to other users within your organisation. Each user will require a Power BI Pro licence and this is activated within the administration of Office 365. For larger organisations, Power BI is also offered as a capacity licence with Microsoft Fabric. However, capacity licencing should only be considered for organisations approaching 1,000 or more Power BI users. Further information regarding licencing costs can be found at the following link: https://powerbi.microsoft.com/pricing/