Is there a way in asp.net to limit the access to a web page only from localhost?
If you want to do this for a "web page" then I'd use IsLocal, but if you want a subdirectory solution I'd use Url Rewrite 2. http://www.microsoft.com/web/gallery/install.aspx?appid=urlrewrite2. If you don't have this installed already, go and get it as it's very useful. I believe it will be standard on IIS8.
Then add this to your web.config under