Contacts is a social, mundane advantage where you "have an associate who provides you with useful information, or who does small (pick any two of “quick,” “nonhazardous,” and “inexpensive”) favors for you. (Basic Set, pp. 44-45)
Cost is effected by Effective Skill, Frequency of Appearance, and Reliability.
Money given to the contact can improve Reliability up to (but not beyond) Usually Reliable.
- On effective skill versus actual skill 
- On high effective skill levels, and whether Contacts or Allies is suitable for a character 
- On permissible favors 
- On the range of the chosen skill 
- On its representation in Wealth