Wikipedia is free but it is not cheap (the amount of information and quality is simply amazing).Advise in StackOverflow is free but we never say/feel it is cheap.
Free is something valuable you give with "no strings attached" to convey that you value the relationship and association. If all the free you give is not valuable (or literally of no use), then the free becomes cheap. It, then, spoils the relationship/association.
Certainly, free and cheap are two different/extreme/opposite experiences.
