Possible? -- for me, maybe. 11x9 is going to be super close to too big to fit on my printer's bed, but there are certainly bigger printers out there.
Cost -- probably not more than a few bucks in filament. What type filament? Good question. Probably something less brittle / more impact resistant than the usual stuff. PETG would be pretty good. I think it would hold up
Engineering time/ test fitting /failed prints... lol... priceless.
On a large scale it seems like it's be best done like the stock coil cover -- injection molded probably? Another thought is ABS vacuum forming, which, if you are crafty, you might be able to do yourself...
Let me see if my bed's big enough, I like a challenge. Are you still wanting nox coil ear stiffeners? Those I *can* do.
Edit: Nope -- in my mind's eye it was oval, but no, it's basically an 11" circle. Too big for my printer.
sorry