If you are looking for the lowest cost, fully-featured Web server for the internet, look no further than Windows Web Server 2008, which is the enhanced version of Windows server specifically built for internet Web sites. It supports the full hardware specs of Standard Server (4 proc and 32GB RAM), has the full IIS7 Web Server feature-set, supports SharePoint and Windows Media Services, and even allows for local SQL Server installs to support Web applications. To compare it to other Windows 2008 editions, go here.
If you are ready to buy, Windows Web Server 2008 is available for purchase online and through all of the major OEMs. If you are a do-it-yourself kind of guy, check out NewEgg's listing for an OEM license here for $349, or purchase the full retail copy on Amazon for $429.
Once you've got Windows 2008 Web server installed on your PC/server, be sure to download the Microsoft Web Platform Installer to help you get IIS7, ASP.NET, SQL Server and even Visual Web Developer Express installed quickly!