Normally £240. Found this in an email they sent to D of E leaders and mountain rescue team leaders. The software to display, manage, print and export to GPS is a free download.
As I understand it, while Mapyx Quo can export user data to any GPS that accepts any of the file formats it supports, it can only export the map itself to a GPS or app that has a Mapyx Quo license installed. So beware: don't assume that just because your GPS has a colour screen, it can import these maps! If I've got this wrong, I welcome correction in the comments (if these maps could be used with Garmin boxes, this would be an even hotter deal, as Garmin charge £299 for OS GB 1:25k).