The stock Animate Dead and Create Undead aren't very good unless you want a horde of lesser undead cluttering up your battle map. I like what I see here, and think it's reasonably balanced. It gives the Necromancer class features that don't rely on having a bunch of low-level mooks following him around, as well as the option to support a few higher-tier undead for a price. The 9th level spell included may be a bit too powerful, BUT considering that the published 9th level spells range from a low end of Weird up to True Polymorph or Meteor Storm, it's probably not too far out of whack.

I would allow this as written in my campaign.

I really like the options this provides for expanding the Necromancer's options over the PHB version without creating an entirely new sub-class. Well done.