university of missouri high school also has inexpensive classes and some specifically listed for "gifted". I haven't tried it but I know it's well-regarded. Also Brigham Young. Some other providers are APEX learning and Aventa. I think the APEX was expensive (maybe $600 for algebra 1 or 2 course) when I looked into it, but it's still cheaper than JHU or EPGY (both of which we've tried & liked but are definitely expensive)