SharePoint Server can be delivered through Office 365 at extremely low and spread cost, but often the need is for on-premises installations – for controlled configuration, maintenance, performance and security. This can get expensive, but we’ll try and help keep cost down.
SharePoint Foundation is free and runs on Windows Server 2008 onwards, and can often fulfill core business requirements on its own – it can even be used for multi-server tiered farms. Plus, SharePoint (all Editions) can still work fine with the free SQL Server Express edition (contact us if unsure of requirements) – although eventually your data or usage logs will hit the 10GB database limit and become a problem solved by upgrading to SQL Standard Edition.
Some good news at least is that the Internet Sites licence (previously around £10K) is scrapped so you can extend relevant parts of your sites to external partners and users for free – a rare bonus from Microsoft!
Standard CALs (Client Access Licences) are required for each internal user account accessing any number of your SharePoint Servers. Enterprise CALs are added on top to provide particular users with that extra functionality – Business Intelligence PerformancePoint, Excel Services etc.
Compare functionality between Standard and Enterprise – somewhat buried away after O365 3/4ths down http://technet.microsoft.com/en-us/library/jj819267.aspx under the On-Premises section.