i whack bushes on 3 separate accounts (cos im addicted). so i am well aware that different side quests require energy at different levels depending on the level of the player. none of my accounts had gone down the rabbit hole and i decided to start that quest on all 3 accounts this morning. at level 90 the bushes and critters down there require 10 and 11 energy to whack. I had to level up my spell whack to accomodate. on another account that is at level 96, the bushes and critters and bushes down there only require 8 and 9 energy to whack. that seems backward to me.

What determines it is your Level, all those mini zones cost me 17 & 18 per Bush. It had been mentioned that those might 'cost' the value of the Bushes you were doing when you first started those mini-zones, but that it might go up as you go up.

But like I said, it's WHEN you first entered those areas.
I imagine that your Level 90 account just started those areas while your Level 96 perhaps started those dozens of Levels ago.
But I also kind of implied that it's wonky. I, and many other high level players first started those when those were first created and we were already at max of at that time perhaps 110 and bushes costing only 16 & 17. All those areas for me cost 17 & 18 now.