There is no numeric answer to this; there are too many variables.
First, how generous do you wish to be? Do you want to give a lavish gift, a moderate gift, or a modest gift? That would depend on the relationship with the recipient, the occasion, and whatever else may be relevant.
Second, what amount would be lavish or modest varies from person to person. A $25 electronic gadget might be a lavish gift if given by a struggling college student, but would be cheap coming from a well off professional.