The cost to upgrade to Business Class on Korean Air can vary depending on various factors such as the route, availability, and fare class of your original ticket. Unfortunately, as an AI language model, I don't have access to real-time pricing information. It is recommended to directly contact korean air first class upgrade or visit their official website to inquire about the specific cost and eligibility for upgrading to Business Class on your particular flight. The airline's customer service representatives will be able to provide you with accurate and up-to-date information regarding the upgrade cost and any requirements that may apply.