Average Salary: $52,000
Expected Lifetime Earnings: $2,170,896
Due to 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), your salary 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 just over $52,000 annually, which isn't bad at all for a career path that allows you to follow your passions (source). You might make less than the average if you're just starting out, and will definitely make less than that if you're trying to make it as a sound editor in a smaller city—Omaha, for example. (Pretty sure the last movie filmed there was Boys Town, circa 1938.)
If you're in high demand in the biz and are working on big blockbusters, you could be looking at an annual salary that easily reaches 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, Ebenezer Scrooge-style.