I would say that, if its always been your dream to make documentaries, and you're willing to make the sacrifices that go with being in show biz, you should go for it. Succeeding in TV or film requires a thick skin and huge amounts of patience and persistence, because you're competing for jobs against all the people for whom it has always been a dream. I'm sorry my tone here has been so relentlessly downbeat, but I figured you asked because you wanted an honest answer. The range is so variable that there's almost no way to answer this question. I don't really know how much less.
Capable editors are highly in demand, and the pay scale and experience requirements reflect that.
I had always wanted to work in television, even when I was in grade school. When I was in college, at UC Berkeley, I started working at the university's radio station, and that led to many years working in TV news, as a reporter, weatherman, news cameraman, and editor. Eventually, by the early '90s, I was bored by local TV news and wanted to do more. After twelve long, hard weeks, I finished that pilot, and it was so good that MTV bought the show, and now it's on every week. That was the last time I worked for MTV, but I've been very busy doing shows for other networks like Discovery and Travel Channel and History Channel.