I spent $1,600 building a sauna. Since I finished it, I've been doing sessions a day, a morning and a just before bed sauna. I haven't got my first electric bill or water bill yet. I've been taking cold showers after each sauna (first time in my life, I was always a hot as I can stand it shower guy) I expect on going electric costs related to the Sauna use. If I keep up the 2 times a day routine, it's near $1.20 a day for electricity.
Here's a picture, I hope to put a skin on the door and window in the door, but I'm pretty slow at additional work now that it is functional.