Currently SharePoint Portal Server (SPS) uses a Client Access License (CAL) scheme. This means that each and every user needs to have a CAL in order to use SPS. It does not matter if the user uses the Web Folder or the Portal interface, they still need a CAL.
The Server License is listed at $3,999 per server without CALs (not per processor) and $72/CAL. The actual cost for the Server License and CAL varies depending on your licensing agreement with Microsoft. I would advice to contact your Microsoft representative for your actual cost. A good resource for this topic is: http://www.microsoft.com/licensing (SPPS 2001 - Sales Guide)