Need 850W+ PSU

I'm thinking of upgrading to a crossfire setup working out how much it will cost me
100% LOAD
XFX R9 280x=360
XFX R9 280x=360
Intel i5 4430=84
Motherboard=50
854 Watts

10-20% LOAD
XFX R9 280x=50
XFX R9 280x=50
Intel i5 4430=30
Motherboard=50
100-150 Watts