There are probably a few experimental case designs that aren’t available to consumers with hypothetical price tags that would send you running for the hills to live a simple life in an Amish community.
In terms of what’s available to the public, the most expensive is the spherical In Win WINBOT PC Case, costing a cool 1K. Coming in second, we have the Corsair Obsidian Series 1000 D, which will set you back something to the tune of $645.