In a thread to the official WoW Classic forums from anqilan's blog

Blizzard Reduces Price Of WoW Burning Crusade Classic Cloning Fee After Player Outcry

World of Warcraft Classic's upcoming character cloning service is set to have prices reduced following a protest by players buy WoTLK Gold. The cost to copy the character's individual traits so that it can be used simultaneously on WoW Classic Era and future Burning Crusade Classic realms will start at $15. down from the previous announcement of $35 that Blizzard had previously made.

All current WoW Classic realms will be immediately converted to play the Burning Crusade expansion with the introduction of the Burning Crusade pre-patch on May 18. At that time the players will need to select on a character-by-character basis whether to join the Burning Crusade servers or to transfer into Classic Era realms that won't move on to the next expansion. Cloning a character to pay the price of the transaction allows the character to play two versions of the game.

World of Warcraft Classic: Burning Crusade : Burning Crusade Reveal

In a thread to the official WoW Classic forums, Blizzard outlined their original reasoning for the charge of $35. "This option of providing players with a second copy of a character in a different game--is completely new for us." the post reads. "Our original idea of the worth of this service was in the way that we cost other services and items that are optional cheap WoW WoTLK Classic Gold. We want people who pick Classic Era realms to feel as though their choice comes with the assurance that they'll have the ability to create a relationship with Warcraft and guilds with other players who they can count on.