Instead of starting a business, you could invest that money elsewhere. Ideally, the device would be fabricated with low-skilled labor. Custom adjustments should be minimized. The electrical design should allow for likely variations in component values. Components with loose tolerance specs should be used wherever possible, and precision components should be specified only if needed.
Mechanical issues are often responsible for much of the cost of production.
The device should be designed with this fact in mind. The question here is whether or not you can maintain profitable operation over a reasonable period of time. In other words, it is possible that only 1000 people in the world want your widget, but they want it badly. Thus, the first year your sales would be 1000 widgets at a good profit margin, but the the next year sales might to drop to 10. Restoration of volume would have to await the introduction of a new and improved product or the demise of the original widgets.