Well, the cost of Christmas lights can vary greatly depending on the type of lights, the length, and the quality. Generally, a set of 50 lights can cost anywhere from $5 to $10, while a set of 200 lights can cost $15 to $30. For a complete set with several strings of lights, you may be looking at spending anywhere from $20 to $50. But if you're looking for the most energy-efficient and cost-effective option, you may want to consider solar-powered Christmas lights.