As of this writing it appears that the paid character boost will be priced at $60. Since this was taken down quickly and with no comment by Blizzard, it seems fair to say the following:
- This was clearly not intended to be visible yet.
- No announcement has been made officially about the actual price.
- The pre-orders for Warlords of Draenor are not even available yet, so it's unlikely that the paid option will be sooner than those.