If you are not using a central transformer, then the cost will be solely based on the type of lights you use. We have done a little research about LED lights and found that a 4.8-foot strand of medium-density amber LED Christmas lights costs $32.95, and a 4.8-foot strand of medium-density clear Christmas Smart LED Strip Lights costs $29.99. With this, we can conclude that LED Christmas lights, which are much more energy efficient than neon Christmas lights and consume about 1/3 to 1/4 as much electricity as neon Christmas lights, cost about $15 to $30 per string, depending on the style you choose.