It costs £88,000 ($110,000) to fully upgrade a character in Diablo Immortal.
Players in Diablo Immortal have three progression pillars: XP level, equipment level, and Legendary Gems. The first two are pretty standard fare in any RPG-type game, but collating Legendary Gems can be a costly and convoluted process as the way you get them is randomised and often exceedingly rare… and right now, it seems as though F2P players cannot earn them at all.