Let's see...
My servers (tiny/mini/micros) in total are about... 600W or so. Two NASs, about 15-20W a piece.
I spend a out $150/mo in electricity, but my hot water/HVAC/etc are the big power draw. I'd say about $40-50/mo is what I'm spending on powering the servers in my office.
Definitely puts off some heat, but that's partially because it's all in one rack, and I've got a bunch of other work hardware in there. It's about 2 degrees warmer in my office than the rest of my home, but I also have air cycling all the time since it's a single unit HVAC and I need to keep the air moving to keep it all the right temp in the other rooms anyway (AC will come on more often otherwise, even without my rack).
So that in 15 or so years, a class action lawsuit completes where Google now provides you with a whole $10 coupon to the play store and a check for $0.65.