Gmoto, agreed you are spot on but we know she's on a budget. But with
null caller it will feed kalitas for now until she gets a replacement. She also doesn't have to use its ability all the time.
Agree that
Sol Ring is a staple to commander deck. Not really an expensive card.
Now the card I suggest and why. First it's Median: $4.46 on tcg so basically 5 bucks it cost.
The card is
Endless Ranks of the Dead and you can go wide with zombies and go big with vampires.
Just need 2 zombies on the field and
Endless Ranks of the Dead will get out of hand unchecked.
2 zombies becomes 3, then becomes 4, then becomes 6, then becomes 9, then becomes 13, and so forth.
Nothing wrong with an army to support big growing vampires.