He may make 50$ per month but he must pay at least as much for power
That's right. Even a single GPU running for a whole month will cost you $10+. You'll buy a $1000 PC and have it running all day mining and buzzing. You won't be able to use it for much. After a month you'll get $40 back, great. Is it worth it? You could get more than that by using this PC to write articles, trade or something.