The cost to upgrade to Business Class on Eva Air can vary depending on several factors, including the route, availability, and fare class of your original ticket. It is recommended to contact Eva Air directly or check their website for the most accurate and up-to-date information regarding the Eva Air Upgrade to Business Class. By providing specific details such as your departure and arrival airports, travel dates, and booking class, Eva Air's customer service or online booking system will be able to provide you with the precise upgrade price for your particular flight.