Despite Eye-Popping $3.5 Million Price Tag For Gene Therapy Hemgenix, Budget Impact For Most Payers Will Be Relatively Small The first gene therapy for hemophilia B, Hemgenix, will have a list price of $3.5 million per use. This sets a new record for the most expensive single-use gene therapy in the U.S. In spite of the very high price tag, the budgetary impact of the product for most payers will be comparatively small.