good idea on securing the display and not trusting the PC OS. But I think your bill of materials (BoM) cost will be closer to $12-15 - so at your potential volumes you might need to retail at more like $40-50 in order to cover your development, production, tooling, and distribution costs and make a dollar per device for yourself. Just a heads up. Also if you open source your software the only intellectual property you've got left is in adding the display to the device nicely (which usb stick providers don't do because it would make the product too expensive), so watch out for competition too...