You need to give more information on what you are building. How many users are you trying to cater for? Are these applications going to be accessible over the internet? I would strongly recommend that you install WSS for yourself and evaluate the features and the costs.
WSS provides a basic collaboration infrastructure over and above the services available for ASP.NET. Licencing costs can be quite expensive for internet use, but that is relative to your revenues. Features like publishing are only available in MOSS so your CMS/localization requirements may not be satisfied with WSS. Authentication is provided in ASP.NET and WSS simply provides a mechanism for managing users and setting authorization.