quote Strayfire

2X Intelligence + Race/Birthsign bonuses. 100 Intelligence + Atronach Birthsign + High Elf Species = 450 Magicka. 5 +50 Magicka Sigil Stones = 250 + 450 = 700 Magicka. Also, the higher the respective skill (i.e. Destruction), the lower spells under that skill cost. If you had 100 Destruction, that spell would cost a lot less. Don't forget Fortify Magicka spells either.

I got a 50 Magicka ring from a shop in Bravil, lowered Strength and Endurance by a factor of 10 however, also got a +25 magicka ring I think had something like absorb magicka or something, so that is +75 magicka there, as well as necklace . You can exceed 100 Intelligence of course with fortify intelligence, if you have full light armour with fortify intelligence, probably looking about +40~+60 intelligence, so possibly about 210 magicka from equipment ... using fortify intelligence and fortify magika spells, well I'd hate to say it but you could probably break 1K magicka >.>.

As a question, what dose the atronach(sp) Runestone give, I know the lady runestone gets a greater power that gives 20 Willpower and Intelligence for 120 seconds =P...

Skill reduces magicka cost , remember this, Flare at level 5 destruction costs like 12 Magicka, by level 50 destruction will only cost like 6 Magicka. However Flame Bolt costs about 70 magicka at level 25 destruction but only about 50 at level 50 destruction. Greater the magicka cost the greater the reductions =P.

If you see a spell that costs like 800 Magicka, it's probably out of your skill range anyway, since your probably like level 15 in that skill whilst the spell requires like level 75 or 100. If you make a hugely overpowered spell however and it costs that whilst you are at level 100, then you'll really need that magicka cost, but if a spell is that overpowered might only be used in desperate situtations to quickly clear out an enemy.