These changes will be in the first "resting hamster" build: generally speaking, if a transmutation benefits a demon, its cost is calculated based on that demon's starting level, not its current one.
Affected transmutations are:
Copy Ability (unless summoner is the target)
Fuse Demon
Restore Demon
Revelation
Unaffected transmutations are:
Copy Ability (if summoner is the target)
Transpose Soul
Soul Armor
Additionally, Fuse Demons has been made 25% cheaper to begin with, but Revelation was increased in price by 50%. So, Fuse Demons will be *significantly* cheaper than it is at the moment, especially on demons who've leveled a bit. Revelation will be more expensive... but this can be offset by letting the demon level more before using it.
So why am I not worried people may keep the same demons forever?
Well, remember, demons start to level slower the further they get from their starting level. A demon that began at Level 1 will find going from, say, 13 to 14, a much more challenging climb than a demon that started at Level 13 would. Notably, the penalties are relatively mild until +10 from starting level, but start to get nastier after that.
Also, a final pair of notes related to enemy summoners: starting level refers to what level that demon would be if it spawned in the wild: demons owned by enemy summoners that are higher level do not consider that higher level to be their starting level. And, these pricing changes have been factored in for summoners too: you will generally see them having used Copy Ability and Fuse Demon more often (and Revelation a bit less.)