Looking at the Cryptek model, I'd start with a triarch praetorian torso for the more built-out upper body, a deathmark head, and go from there, filling out the back with kitbashery. looks like the right hand is some kind of orb device, which you could kitbash from some parts for the grave harnesses in the praetorian kit. for the large staff, the lychguard from the same kit seem to carry a somewhat similar looking weapon.

TLDR: Buy 2 lychguard boxes, and trade for some deathmark heads from someone, and you are about 90% set... that's like half the price.