The method that OP described doesn't involve any type of additional electricity cost, since it doesn't require actual equipment to mine bitcoin Instead, you pay a "share," if you will, that's hosted by someone else and the you get a % of the earning, by buying (with a credit card) and selling those "shares" (cloud miners).
But it looks like they are not selling miners anymore...at least not in stores where you could pay with a credit card, just Bitcoins.
We've actually started Bitcoin mining over the winter, and plan to stop when summer rolls around. The extra heat from all the mining servers in the house is welcome!
I figure the money I'm saving on oil heat is an MS bonus. I don't have solid numbers yet, since we just started, but I suspect this will be a big money maker for us.