If there is saver award availability in economy, but only standard award availability in business, can I book the economy ticket and later upgrade to business with miles? If that can be done, would the upgrade cost the difference between saver bus and saver economy or is that wishful thinking?
Ex. Economy ticket for 40,000 and business class not available for 60,000 (can get it for 150,000). Can I book the 40,000 and pay 20,000 to upgrade? Or would I have to pay 110,000 to upgrade?