A person with what amount of money in his pocket would you consider poor?

A poor person is unlikely to be able to have free / extra money to invest in a bitcoin, much less store it. Very soon he will need to extract this money and the double conversion back and forth will make him even poorer (money -> bitcoin <- money) and forth will make him even poorer. I believe that for people with such material wealth, they should focus on building their financial stability (increasing income) and only when there is excess money, invest in a bitcoin.

In fact, there is no minimum or maximum in investing in bitcoin. That's the beauty of bitcoin, you can invest even a couple of bucks.