Also applies to Deathwing - Like Draigowing, you just need 1 metal model (Belial) and then 20 plastic Terminators, which can be found reasonably cheaply.
Of the three, Deathwing is probably the cheapest to buy since you can use generic Terminators which are available in abundance on eBay and the likes, whereas the other two require specific (and fairly recent) models that aren't so easy to get hold of outside of a GW Store.