The current system relies on you paying a full amount of AC based on your level in order to be able to change your skill tree.
My idea is to be able to have a method that would allow the player to change their skill tree individually without having to reset it completely. Simply implement a system that per every skill you wish to reset it would cost a certain amount of AC based on your level.
Example 1
Lets assume the player is Level 10. (10 skill points) Let's also assume that it cost 10,000 AC to reset the whole tree.
Equation: 10,000/10 = 1,000*2 = 2,000 This would be the amount per every skill point you wish removed.
You're probably wondering, why 2,000 and not 1,000? The idea is simply to allow the player to redo only parts of a skill tree, NOT the entire thing. If he wishes to redo the whole tree, then it'll be better to just have it reset completely.
Example 2 (In case the number 10 lost you, here's another one)
Let's assume the player is Level 25. (25 skill points) Let's also assume it would cost 200,000 AC to reset the whole tree at this level.
Equation: 200,000/25= 8,000*2= 16,000 At level 25, it would cost 16,000 per skill removed.
TL;DR
Implement an alternative system that would allow higher leveled players to redo and remove skill points without having to spend the FULL amount.