DH and I set a budget for each other, depending on how much cash we have at the time. It might be $50 each or it might be $500 (usually less though).

For extended family (ie, our siblings and parents and cousins and neices and nephews) we have a rule - we only buy pressies for those we see on christmas day (too many otherwise). We spend between $20-35 per person, depending on the person in question and how easy they are to buy for. We occaisionally spend more on my parents and buy them a combined pressie.