I worked for a company that made custom cases a few years ago, and we weren't able to sell a single one. I believe our case was costing us something like $3-400 to produce(custom frame & paint job are expensive). My boss tried to enter the market as a completely assembled PC gaming machine to hide that cost, but it was easy for knowledgeable builders to price out the same rig on Newegg to figure out the cost of the case.
There are just so many options from great case makers and professional modders already on the scene, it's a tough market! There is only a small percentage willing to spent more than $100 on a case, and the higher you go over that, the more discerning the buyers are. We weren't able to pull it off but I wish you the best of luck!