I haven't found the answer to this anywhere else, but if I have the Expert Destruction perk that reduces magicka cost of Expert-level destruction spells by 50%, and I enchant two pieces of armor with a further 50% magicka cost reduction on destruction spells, will that be equivalent to reducing their magicka cost by 100%, or will it take the 50% reduced cast-cost that my perk gives me and reduce that by 50%, thereby giving me only 25% reduced cost?

This greatly changes the enchantments I'd like to do, so any help would be appreciated.

They add, completely eliminating magicka cost for that school and breaking the laws of thermomagickadynamics. Congrats, you broke the universe, furthered entropy, and everyone will die a little sooner because of it.

They operate separately. Ignore the above poster.

50% from perks and 50% from enchants will equal 75% reduction.