This is a good question, I was wondering the same thing about a year ago. Although I grow in natural light, so it isn't an issue for me right now. I will try to look for that type of info later tonight if I can. I think one of the big reasons it is not readily available is because electricity costs vary so much from one area to another, and even sometimes with the season like summers when everyone is running their AC. I can tell you how to figure out the exact cost of the lighting once you have it running, but it needs to be plunged in first.
I could be wrong but as I understand it, MH and
hps are the most expensive to run. Then I would guess that florescent would be next, and lastly
led would likely be the cheapest to run. There are also other considerations to consider like heat buildup with MH and HPS, and the electricity needed to run fans to get rid of it. Also the the fact that florescent cant put out the same type of intensity (needing more to do the same job). LED may be the cheapest to run but not to buy that I know of. They all have there pro's and con's. Is it possible to grow in natural light?