For example, you could get all cost reduction perks, max out Enchanter and Extra Effect perks for the gear below...
Head: Fortify Destruction 25% / Fortify Restoration 25%
Body: Fortify Destruction 25% / Fortify Alteration 25%
Ring: Fortify Destruction 25% / Fortify Illusion 25%
Neck: Fortify Destruction 25% / Fortify Conjuration 25%
An alternative is to use the Arch-mages robes which gives 15% in all 5 schools, however as there are only 4 slots you can apply the enchants too and that takes one, it makes it impossible for free spells in any school... then again it's got a +50 magicka effect on it too.
So that would be:
Head: Fortify Destruction 25% / Fortify Alteration 25%
Body: Fortify Destruction 15% / Fortify Restoration 15% / Fortify Alteration 15% / Fortify Illusion 15% / Fortify Conjuration 15% / Fortify Magicka +50 / Magicka Regeneration +100%
Ring: Fortify Destruction 25% / Fortify Conjuration 25%
Neck: Fortify Restoration 25% / Fortify Illusion 25%
This gives possibly the most optimum reductions if you're going after all schools. Tho Lancifer's example gives the the most practical reductions (since destruction is probably going to be the most used spell type in battle).
From what I've given you get from enchantments, Fortify Destruction 65%, Fortify Restoration/Alteration/Illusion/Conjuration 40%. Total fortification : 225%
From Lancifer's Example Fortify Destruction 100%, Restoration/Alteration/Illusion/Conjuration 25%. Total fortification 200%
I offer this as an alternative because to me, fortify destruction 100% just means you can spam dual-cast stunning expert single target spells as you like, constantly with no cost and thus feels a bit broken. Then again destruction is under powered so... if you feel that too much going for destruction 100% maybe for you.
Notably I believe these numbers are based off of 100 Enchanting skill with all relevant enchanting perks, however alchemy also has a potion effect, Fortify Enchantment that maybe able to push above 25% fortification for enchantments, I haven't tried it myself tho.