Flat Pitch Power Required
If memory serves me correctly, it takes approximately 17%-20% to turn the B-206 rotor at 100%. That would be somewhere between 50 and 60 ESHP. This would get you to your starting point. Your system would have no accessories (i.e. hydraulic pumps generators or tail rotor take off) so the number would be somewhat reduced from the 50 to 60 ESHP.