If you had a decent CnC, or access to one you could make yourself a lot of money. Although I'm not sure how you go about patents
Custom frames would be good, 1-off's could make decent money and a good range of triggers, snatch grips, frms etc would do well. Currently those that make custom triggers etc tend to stick to one or 2 markers and don't like to stray too far.
How long does it take to create something like the Ego bodies?