The other thing that can be done to create a “more money, fewer cards” feel (if that’s the desired direction ) is have things just cost less gold than they “should.” So, the Zerg starter could be:
3 cost unit: Queen (1/3 anti-air. Queen can cast Level 0 Zerg spells as if it were a hero)
3 cost unit: Spine Crawler (3/3. Can’t attack)
2 cost unit: Baneling (3/1 Sparkshot. Attacks: sacrifice this after the attack)
2 cost unit: Roach (2/2 Sparkshot)
1 cost unit: Drone (1/1 Tap to make one gold)
0 cost unit: Zergling (1/1 does not gain bonuses from patrolling)
2 cost spell: Zergling Swarm (Make 2 Zergling tokens; they are 1/1 who do not gain bonuses from patrolling)
1 cost ongoing spell/upgrade: Creep Tumor (Your Zerglings gain Haste and can get patrol bonuses)
1 cost ongoing spell/upgrade: Larva Reserve (Tap, Sacrifice: Draw a card)
A building of some sort
A 3 cost Ravager unit, replacing Queen or Spine Crawler
A Spore Crawler unit (Anti Air, Can’t Attack, Detector?/Cannot be bypassed by Stealth/Invisiblity)
Note that there is nothing wrong with copying over an existing card at the appropriate tech level if the flavor fits.