" If we want to define how “open” any industry is, we should start with a number: the cost of entry. By this we simply mean the monetary cost of getting into the business with a reasonable shot at reaching customers. Is it in the neighborhood of $100? $10,000? Or more like $1 billion? Whatever the magnitude, that number, most definitively, is what determines whether an industry is open or closed. "

― Tim Wu , The Master Switch: The Rise and Fall of Information Empires