The best keyboard and mouse for power consomption are the logitech K750 (keyboard) and mouse logitech M510
Why? You can program the wireless unify device that talk with the mouse or keyboard to talk to both device, when i buy these to device, I programmed both wireless adapter from my mac, so one is on my mac and the other on the pi.
It work really good on the pi once programmed, the consumption is so minime, even on a 1watts charger adapter it work fine, i believe the consumption is less then 200 ma.
Anyway, here some pic of the pi and the keyboard and mouse