>>10559580the Toybiz Hulkbuster would serve as the base figure. They're cheap nowadays, usually between 40 to 60 bucks. Swap out the arms with those of a hulk baf, recycling the hulkbuster's gauntlets into Horrigan's arm guards. Then swap the legs out for a DCUC CnC Stel or Stripe's legs and then that would complete the body. The head and weapons would be 3D printed and the shoulder pads would have to be scratch built from styrene probably.
For what its worth I also had a recipe in mind for Liberty Prime. You'd take an old mega bloks techbot (captain america or lizard should do) and then just build up the negative space with scrap plastic and fodder. The head, lower arms, and lower legs could be 3D printed and added on later.