If we implement SharePoint Foundation, what are the licensing requirements and implications to have it setup as an Extranet environment?
The key question is: Are the users authenticated in any way? If the answer is 'no', then you are OK because SPF requires no user license. If 'yes', then keep reading.
I am not a licensing expert, but here’s what I've been able to piece together:
More info: Windows Server Licensing FAQ
Here is detailed guidance on licensing SharePoint products:
For internal users they must have a valid windows server license. In most scenarios this is true for all users otherwise you are not allowed to connect to any windows server box (fileshare, ...). Thats why SharePoint Foundation is mostly referenced as "Free".
If external useres (not from your company/organization) are using sharepoint they need a valid license if they have an AD account. so there is no real difference:
If anonymous users or user authenticated against SQL or other sources a Windows Server External COnnector license is required: http://www.microsoft.com/windowsserver2008/en/us/external-connectors.aspx
I don't see the need for a "SharePoint Server 2010 for Internet Sites" (FIS) license.
You can check the licensing portal for some sample prices. Select guided quote and from the drop down "server" for all sharepoint options. http://www.microsoft.com/licensing/mla/product.aspx
As long as you go with SQL Express no additional license is required. If you upgrade to a bigger SQL license you will need a CPU license if you need a externeal connector license :-)