Singh did not include the Surface keyboard-cum-cover, dubbed "Touch Cover" by Microsoft, in his estimate. On its Surface website, Microsoft says, "Surface comes with ... a revolutionary, 3mm thin, pressure sensitive cover that doubles as a fully functioning keyboard and trackpad," referring to the Touch Cover.

Microsoft will also sell a more capable keyboard/cover as an accessory. Called the "Type Cover," it is thicker and provides some key travel for a more notebook-like feel.

"Estimating the BOM of the cover is a major challenge as the cost drivers are a bit of a shot in the dark," acknowledged Singh in an email reply to questions today. "But based on pricing trends for similar accessories, I'd say it could be priced around $50-$100."

Singh also estimated the BOM of the Surface Pro, the tablet powered by Windows 8 that Microsoft will launch in late January 2013.

Unlike the Surface RT, the Pro will run not only touch-style, tablet apps, but also traditional Windows software, such as Adobe Photoshop, the full version of Microsoft Office and PC games.