There's no upgrade price, they are treated as two completely separate versions.
Viewing post in Upgrade from Freerider to Recharged
You can view Recharged as a sort of DLC (although it works fully on itself). There were several reasons I decided to make Recharged a separate version, one being that the file size of the original needed to be kept small, and, it was necessary to keep it running reasonably smooth even on older hardware and mobile devices. With Recharged I wanted to be able to work without restrictions and add as nice looking sceneries as possible. Email fpvfreerider@gmail.com.