Since Illusion really isn't Standalone (Though you could combine it with weapon skills instead of other Schools to finish that last guy) it actually works with not enchanting up to freebie. A Wizard can Fortify Alteration, Conjuration, and Illusion (A fantastic combo, BTW) spread amongst 3 different items with extra effect (and wearing Vokun) None of them up to 100%, but I've gotten around 50s in 3 schools with nothing more than 100 Enchant, and the half off Perks. (Layer, don't stack, so 50% of 50% leaves 25% base casting cost.) I feel that this is a lot closer to the spirit of crafting a mage build than Feuer Frei Stunmer.
Just because I like posting Builds, (and haven't for a while) here's a good Battlemage for this kind of setup:
Skyrim Perk Calculator - Plan the perks for your Skyrim character before spending them! I used Bound Bow as a Conjuration/Archery trainer, and soul harvester until I could clean out High Gate Ruins, Labrynthian, Ironbind Barrow, and Enchant a decent Ebony Bow. The usual Firey Souls/Absorb Health on that, with 45/73% off the three schools, and Resistance on the Ebony/Robes (actually Ulfric's Clothes) and Vokun on top. High prep, drop a battle appropriate summon, (or 2) and Ebony Flesh, then switch to the bow to support it, with Illusion Effects available as needed. Note, this was an old build (which I don't have screencaps, or a save to pose from) before Aspect of terror got patched, and no Sneak, so I took the midline to MotM instead of Quiet Casting...
Also, Twin Souls is optional, there's a point available there, but I invested 1/1/1 in H/M/S (about 300 each with an Altmer) so I had neither the time, nor Magicka to double summon, anyway. I also warn you, this is a pretty unstoppable Master build if you know how to play it. All strengths, no real weaknesses with the Lord Stone to cap off your Magick Resistance. The other primary Enchantment was Fortify Archery. Stay out of the melee, you've got enough health, and passive defense to soak a lot, but no CQC offense.