How much are mining pools currently spending on mining per BTC?
Power usage per GH/s changes with every new ASIC product.
I believe the Antminer S9 is probably still the state-of-the-art in december 2016. Batch 23 of this miner does 14 TH/s with 1372W +10% (at the wall, with Bitmain’s APW3 PSU,93% efficiency, 25°C ambient temp)
The price for mining hardware changes all the time. But now in december 2016 around 0.12-0.13 USD per GH/s should be expected. That's including the necessary power supply but not including shipping.
Of course there are people on ebay who will sell you a 1 GH/s USB stick for 10 USD. Not only do they cost way too much per GH/s but the power usage per GH/s will also be very high.
The price for electricity of course varies around the world.
Some miners get good deals buying mining hardware in large quantities and have special deals with power companies for very cheap electricity. Those deals will probably not be revealed. So we won't know the actual cost for a big miner to produce one bitcoin.
Keep in mind that some big miners are also manufacturers of bitcoin miners. If customers buy hardware from you, paying for the cost of having the chips designed and put in production, then you can make some extra machines for yourself very cheaply. If you can combine this with a good deal on electricity, then you can mine extremely cheaply. Unfortunately your mining will push up the difficulty which in turn hurts your customers who bought miners from you.