It's not even that expensive either... you're level 65+ that should not be a problem, if you think it is op out of this guild quest... if anything i think gq are way to easy. I understand why, but still very easy.
The best way to deal with that kind of quests is to have more troops than necessary to do adventures or you can pay with gems to complete the quest (some prefer to do that) ...
It will be a lot better when we will get the update with the jump button in barracks to replace them in a reasonable time for now it's patience we need and let's hope we'll get that update before Christmas