Blizzard has confirmed that they are now offering $ 60 level boosts, to immediately bring you all the way up to Level 90.
The new boost is more than the blatant cash grab it looks like, as some fans speculate. 3rd party cheat creators have been making level boosters on their own, so this offer seems intended to run them out of business. It will also help newcomers come closer to the new 100 level cap.
The official line from Blizzard is that they decided on this after receiving customer feedback, but these are likely factors that came up in the feedback as well.