i say 200-300 mil to farm it efficiently
Anyone saying less is smokin crack. You could survive it for less, but you won't be efficient.
I hear a challenge coming on, depends on your idea of efficent. If you want 5 second elite kills sure its not efficient but the 15m set I built was killing elites in 15-30 seconds depending on what affixes they had. I dont know but personally I dont mind spending 15-30 seconds on a elite mob i conciser that efficiency enough.