Because of the off-and-on nature of your work ("on" when you’re working on a film, "off" when the work is done and you're on the lookout for the next one), it really just depends on the size of the projects you're working on, and how many of them you can pack into a calendar year.
The average sound editor makes about $50k annually, which is not bad considering how few days a year you actually work (compared to most other professions), possibly less if you're just starting out, a lot less if you're trying to make it as a sound editor in Omaha. (Pretty sure the last movie filmed there was Boys Town circa 1938.)
If you're in high demand and are working on big, mega-blockbusters, you could be looking at an annual take easily in six figures. And you'll get to spend so much time alone in your editing bay, you can sit there well into the wee hours counting and stacking all your gold coins a la Ebenezer Scrooge.