A level 90 boost will come with the Warlords of Draenor expansion at no cost except for the expansion itself which is $60, but it will only level one character. World of Warcraft Lead Encounter Designer Ion Hazzikostas spoke with Eurogamer about it saying that they didn’t want to force players to buy a second version of the expansion just to get more level 90 boosters. But that once this was available for one character there would be a demand for more.
The $60 price tag was put in place because Blizzard didn’t want to “devalue the accomplishment of levelling.” Additionally there has been concern that with everyone able to purchase the booster no one would ever level anymore. Hazzikostas doesn’t believe this will be the case, partly thanks to the hefty price tag.