I don't see a good reason to prevent low level mages from casting Animate Dead. They will just not be very good at it. So I've made a new version of the spell, which improves as the caster levels.
Spell Level: Cleric, Magic-user, 1st Level
Range: Referee’s Discretion
This spell animates undead from dead bodies. The caster must have corpses available to use this spell. He can use animal corpses if necessary, though small animals are limited to being skeletons or zombies. Mummies must be made from a humanoid creature.
The undead remain until destroyed, and will follow the caster’s commands. Wights and mummies can make a saving throw to escape the caster’s control when they are first created. If they succeed, they can either attack the caster or flee to terrorize the countryside. Only truly mercenary or evil spellcasters will use this spell.
One HD of undead are animated per level of the caster.
Casters are limited in what types of undead they can raise:
1st level: skeletons
2nd level: zombies
3rd level: ghouls
5th level: wights
8th level: mummies