Your total magicka = your inteligence x 2 plus any racial/birthsign bonuses plus any fortify magicka items you have equipped. Increasing your intelligence and adding fortify magicka items will increase your magicka supply.
Endurance(edit fix) Willpower increases the rate at which your magicka regenerates itself, but does not increase the total magicka you have.
The cost to cast a spell goes down dramatically as your skill in the school that governs the spell goes up. Wizards Fury is a destruction spell, so its cost will go down as your destruction skill goes up.