How do I give a spell a constant magicka cost?

[Pancakes22]

I am amking a spell for a mod, and I would like that cost to be a constant 250 magicka. I unticked auto calculate in the spell and set it to 250, but it still goes down. How can I make it a constant 250 magicka no matter what level you have in the school, or whatever else affects spell cost?