These sound easy and tasty.  I would probably make up my own "cornbread mix" rather than using a boxed version.  In a pinch or in a hurry though, measure out 1 cup (8 oz) of a prepared versions if you absolutely don't have time to make your own, and that should do the trick.

http://www.recipetips.com/recipe-cards/t--3680/sweet-onion-corn-muffins.asp?newsid=971