More about site sizing
In a further refinement to the site sizing issue, if you use the advanced search features on Google you can get a better estimate of the actual number of web pages on a site.
site:www.domainname.com will return everything that Google has indexed.
site:www.domainname.com filetype:pdf will return all PDF's that Google has indexed.
You can do the same "filetype:" for other common files like .doc, .ppt, or podcasts and videos. Subtract all these extra file types from your original total and you will have a very good approximation of how many actual web pages a site has and therefore the size of the SiteCM license required.
Of course, a good CMS like SiteCM will allow you to have 1 page of content appearing in several places with different URL's, but these usually only account for a very small number of pages.