One way in which the chaos player can circumvent the need to purchase expensive (metal / but eventually finecast??) versions of chaos havocs is to convert the loyalist devastator squads. This is one of my first attempts at realizing this idea, using a las cannon devastator. Realistically, not much effort has gone in to this conversion. A simple head swap coupled with chaos shoulder pads is rounded off with a gargoyle's head being attached to the end of the las cannon to give it the chaos feeling. This is a simple chop, file and replace job for the regular las cannon terminus.
The one thing that bothers me about this conversion is the backpack: it really doesn't look terribly chaos. But, since I'm eventually intending for this guy to join my Sons of Malice ranks, I'm not sure this would be a problem. The reason being is that the Sons of Malice turned way after the original chaos legions did and they probably had packs like this available to use. That's my narrative and I'm sticking to it!