Stormborn said:....
PS IME people who get paid $s per word are more likely getting a lump sum based on the type rather than length of the article or are fulfilling a contract that works out to X per word, usually where what the magazine is really paying for is the research and legwork that goes into a relatively small article.
You are correct on the aspect that the $+ per word requires interviews and some legwork. This takes much more time than the actual writing. The article length is usually set pretty strictly to X words and you get the flat amount per word, sometimes more if the extra words are interesting. Payment is usually good in this area, rarely does anyone get more than 60 days out, payment due upon acceptance not publication.