Cost per day.

Trained Hirelings
- 3sp gives you 1 trained hireling with 4 skill ranks in 2 skills (Level 1 commoner with 10 int)
- Each additional level of commoner costs 1 sp per day.

Untrained Hirelings
- 1 sp per day (Commoner level 0)

Other NPC classes (Warrior etc)
- 4 sp + 2 sp per level