The purchase of a bump to level 90

The purchase of a bump to level 90 from say level 1 will the cost be the same as a purchase of a bump from level 85 to level 90? I have several Alts I would just love to bump to 90 that I cannot possibly bring myself to level up in Pandaria. I would really like to see a scale for the bumping to 90 for instance X for 1-90 and maybe level 20 to level 90 pays wow gold fr 10% less etc. Without knowing what the cost for this purchase will be I am reluctant to put an actual amount on it. But I would say I would easily pay $5 bucks to bump my 87 to 90. Just a thought.