According to this: $63M to develop the original release or World of Warcraft, plus at least $200M more for all the subsequent releases.

https://mmos.com/editorials/most-expensive-mmorpgs-ever-deve...

Total costs of $200M as of 2008:

https://www.wired.com/2008/09/total-operating/

WoW $60m for initial release, $200m a couple expacks later. The list is missing many games.

Initial development cost of LoL was, I believe, $12-$15m - not very much.

The amount they've poured into it since then, of course, is astronomical.

Surprising that no Blizzard games made the list