No one said getting a pair of Google Glasses would be cheap. They're 15-00 bucks. But on Tuesday, for one day, anyone in the U.S. willing to plunk down the cash could buy a pair off Google's website. Mashable's Chief Correspondent Lance Ulanoff says the sale comes at a critical moment for Glass, which so far has only been available to a small group of developers and other so-called "Glass Explorers". So why limit the sale to just one day?