It all depends on your clients and the specifics of each project. If you want to make a lot of money, you go after certain kinds of clients. As with other kinds of writing, major corporate clients tend to pay the best. However these usually require the most research or reporting work, so in the long run you may not be making a very high rate per hour. Of course smaller companies, independent consultants, institutions, and nonprofit groups usually pay less than major corporate clients.
Some freelancers find that very attractive.
You probably won't be billing by the hour, however. If a project ends up taking far too many hours to complete, you could end up working for slave wages. Having to touch base with 14 industry experts to find news for each issue should be worth more than having to conduct an hour-long Web search once a week. They work well in a pinch if other stories fall through. This can take a lot of time, depending on the publication.