An infographic that can be used for quick reference that details the major differences of the licensing for Cloud (Online) & On Premise versions of Microsoft Dynamics CRM 2015.
Please note that the prices can vary depending on conversion rates and also by Microsoft partners. On Premise prices were based on CRM 2013 (Latest released).
http://www.fmtconsultants.com/products/microsoft-dynamics-crm/microsoft-dynamics-crm-2013/crm-on-premises-pricing-and-licensing/ (& the PDF that can be downloaded)
US Dollar prices converted to GBP prices by xe.com on 25th January 2015.