I'm a full-time freelance writer covering technology, with an emphasis on privacy, security, and digital freedom. I edit an online fitness journal and have covered health and fitness for magazines and websites. I cohost a podcast on Friday news dumps. I write about content marketing and am the producer of PR For Startups, a video course.
Are you talking about travel writing, writing for websites or writing for magazines? It really varies. For magazines, sometimes there are directories in professional groups (such as ASJA or Freelance Success), or paid sites like MediaBistro or Writer's Market (which is also a book). There's even a tumblr called Who Pays Writers? (http://whopays.tumblr.com/) Writer's Market also has a chart of going rates for various projects, though I think what they say for copywriting is a little low.
If you're working individually with a site, I wouldn't go any lower than $1/word or $100/hour. In general, it's a good idea to keep track of your hours so you can begin to calculate pay per hour, though. A magazine that pays 50 cents a word but is easy to work with may have a higher hourly rate than a site which pays $1.50/word but requests a lot of interviews and research and/or multiple rewrites/revisions.