I think you could do okay as a professional CFI, either at a select few schools or as a free lancer in the right place. The problem is that very few could avoid CFI burnout for a whole career. I know I couldn't.

Another option that would pay about the same over the life of a career would be 135 freight. A guy could work into a pretty good deal if he had the seniority and was happy with the base and hours. You won't get rich, but you could have a good QOL while working way less than a CFI.