Lol hey there my friend. I think the large MP costs are a trial/error thing on SE's part. You can more than likely expect these costs to be around half as much soon if the community continues to voice there opinion about it. For some spells anyway.

My best advice right now, is to pick up another class, the great thing about the final fantasy online titles, is that you are not subject to play only one class. Until the pending adjustments are made, if any.

If you want a clear cut reason why they are the way they are, is more than likely because SE was trying to capture the Mages roll as a healer/assist class very definitively, and in doing so, nerfed there solo capabilities so that they would be more reliant on groups, which in tern, would cause them to seek parties.