I kitbashed this priest together yesterday:

Legs and horse from general kit,
torso was left over bit from my captasus conversion
hammer from warriors of chaos
head from flaggelants
could do with a little GS around the wrist but is in no way necessary for it to look good (only better

)
took me about 15 mins to build
btw: it is written that Priests of Sigmar shave their head as a sign of devotion. I don't know if a shaven head is obligatoire or if it's just fashionable among priests