If you are willing to work 90 hrs/wk for $10k salary, why not take a regular 40 hr/wk job for $10k salary (or more even, why limit yourself?), and spend the other 50 hours doing whatever you were going to do?
There are plenty of $10k/yr 40-hour-work-week jobs that don't require any mental load after you clock out, and don't pretend like you won't get anything done in those 50 remaining hours. If you can't build anything with 50 hr/wk to use (which is more than enough for a regular full time job), it seems unreasonable to assume that somehow adding more time would solve the problem.
This assumes we take you at your word that you can be productive for 90 hours, and that you live or are willing to move to a country where $10k/year clock-in-clock-out-and-forget-about-it-work can be found relatively easily.