If they want to use .NET, would you consider Visual Studio Express edition? The express editions (as well as SQL Server Express) are all freely available. If not, you could consider using a simple text editor (e.g. Notepad++) plus Chrome. To keep their training a bit more modern, maybe instead of ASP webforms you could teach them MVC (a much better pattern for web development imho) or use PHP + a MySQL database--the advantage of the latter being that everything's free.