That's a bummer. I think you're seeing the 'black' edition at that price. The regular version's seeing typical Koto reissue. I just scrolled around online, and I'm seeing it for preorder at some places that want between 65-75$.
Metal Gear REX | CollectionDX
Here's my review link.
I can't say much about the Hildolfr because I've never built one, though I have to say it looks amazing, but the Rex is an awesome build.
Have you looked at any Master Grades of that price/size?