Fire protection 1, 2, 3 can all be gotten for one level.
Blast Protection 1, 2, 3 can all be gotten for one level.
Projectile Protection 1, 2, 3, 4 can all be gotten for one level.
Respiration 1 costs only one level.
Aqua Infinity can be gotten for only on level.
Unbreaking 2 and 3 both cost 5 levels.

Thorns, Sharpness, Smite and Looting all seem to be good though.

We need a new formula that works for all of these.

Code to fix this issue was implemented in 1d5e29a. Now @lclc98 does not have an excuse not to fix this :3