In short: Exercise Weapons for mages means the magic training equivalent to drinking 600 Ultimate Mana Potions. The advance of one Magic Level for a mage costs the same number of weapons as a Distance Skill for a Paladin.
For simulations specific numbers I recommend using TibiaWiki's calculator: https://tibia.wikia.com/wiki/Calculatorsthis table I created to show the weapon efficiency: https://tibia.wikia.com/wiki/User%3AMolx/Exercise_Efficiency