As for Mr Weasley in #6, I always got the impression that he was in a low paying position mostly because he loved what he did rather than his pro-muggle politics. While towards the later books his politics did make his job harder, he had no real desire to advance his position. He had a loving wife, children whom he loved with all his heart and who were turning out very well, and a job he really liked. While they would struggle to make ends meet, they managed. They were all perfectly happy with that (well, maybe except for Percy).