TJ here with an idea you can steal. Want a plastic Contemptor Pattern Dreadnought?let's take a look at how GW is making this possible:
So we all saw the leaked imaged of the Adeptus Mechanicus line.


Down in the corner, you can see a somewhat goofy, giant Space-suit robot ...


... which has a datasmith Tech Priest on a 25mm base next to it for scale.


Here is a photo of a Contemptor next to a Marine on 25mm base for scale. Now while we don't know the price of the of the new Kestallan robot, but we do know that a Contemptor body alone is over $48, plus about $28 for the two arms plus whatever shipping you pay, so you are looking at $80+ altogether. The real questions are: 

How much is a Kastellan?

How much effort are you willing to put into a plastic Contemptor conversion? 


So here is an up close look at the Kestallan. Note the similarities in the legs and combat arms (BTW, it also has some kind other arms included). The body is comparable, but not an exact match. The addition of an exhaust system would go far. As far as the head goes. I recommend trying something creative. Obviously take the head away from the robot, then maybe embed a part of a Space Marine head and torso as if his power armor is a sarcophagus. I am sure there are plenty of creative ways to make it work.

I would be super interested in seeing somebody take on this project or even trying to make a robot into a Decimator! In any case, hopefully, you don't just flame me for the clickbait title and as always, comments and ideas are more than welcome.