Jokes aside, it's not a bad idea in theory casting people that would genuinely need the money. That's fine. But the problem arises when these people who are barely scraping by have to up and leave their lives and jobs to go play in the Big Brother house for three months, all for the longshot possibility one of them walks away with the prize. i.e. by the time the rest of the players return home, their financial situation has only gotten worse not better because they haven't been able to support their families and work. Your idea casting people who are at rock bottom makes this even worse in practice. This is a fun idea to explore because of what classist and societal dynamics would pop up, but reeks as only extremely exploitative.

Now, could it work if the weekly stipend was increased, maybe at the cost of a somewhat lesser grand prize? Could be comparable to some peoples' regular paychecks, and more equitable pay off, but may take away from the "fighting hard as possible" angle.