Dude, best of luck. Staring your own shop is harder than the Predators advancing to the WCF. You are going to need enough start up capital to finance equipment, inventory, manufacturing space, insurance and living expenses. It my take up to five years to turn a profit. I truly admire your passion and wish you the best in your endeavors should you decide to pursue it.
I think the key would be having to mass produce them. I'm thinking a lot of those Defender style cases and Defender clones you see sold on Amazon are produced in China.
Flossy in one of his videos recently was talking about that guy who sent him the Wifi only S6 Edge to do drop test with. He said the guy wanted to do Defender style cases and sell them at fraction of the cost but that he didn't have the funding because the investors decided to back out of the idea.
I would think it would be the equipment that would cost a lot of $$. For the price of the equipment and such it would probably be way cheaper and open up a small shop that sells cases such as Spigen, Supcase and such and finding retail space with suitable rent price. The only problem is the only mall near me is a POS and on the decline and except for back to school and christmas there isn't a lot of foot traffic. Even if they have low rent just to get businesses to go there the sales wouldn't be high enough. The better mall is 40 miles to my north or have to go at least 30 miles south.
If it were the mall I lived near while in St. Louis it would be different. Has a lot of foot traffic and younger crowed compared to God's waiting room here in my area of Florida. There is also a lot of cell carrier stores there too which you could take their case sales when someone buys a phone and they see your stand selling no name or Spigen cases for 50 percent cheaper than the $60 otterbox or $45 Tech 21 cases at ATT and Tmobile.
Honestly a large majority of people I see are not using the Otterboxes and other $50 cases but the $20 generic ones you see on Amazon or the junk the Kiosk sell.
These days I actually see just as many people carrying around Spigen and Supcases/Unicorn Beetles as I do Otterbox at least in my area and where I work. I think Otterboxes have got so high priced now and with so many decent generic ones out there you can save more $
If they sold The I Blason Armor Box and Supcases at the time I pre ordered I probably would have stuck with them but Amazon didn't have them in stock yet and with the possibility of the phone coming in early I went and bought the Defender because Best Buy had it almost 3 weeks before the launch date.