You have the right idea. Your problem is here:
Dim message AsString = readHtmlPage(Server.MapPath("repQuotation.aspx"))
Server.MapPath returns a physical path, not a Uri. The HttpWebRequest.Create() method expects a string which points to a Uri -- in other words, a virtual path, not a physical one.
You can test this by passing in any known good URL into your readHtmlPage method:
Dim message AsString = readHtmlPage("http://www.google.com")
This will email you Google's home page.
The other thing to keep in mind that when you email a web page, any links, images, or other resources referenced by relative URLs won't work. Resources have to point to absolute URLs in order to be functional, just as in any external HTML document.
Given that, you probably need to scan the response stream for relative URLs and process them accordingly.