Increase volume on 1 channel of an mp3 similar to Acoutic Labs Audio editor

I've downloaded about 20 odd free ones so far, about half way through trying them out, afraid I might miss this function or miss a good program-

to re-cap, I have several files where one channel was recorded with low audio compared to the other. i want to increase the volume of the low to closer match the other.

The program I mentioned above (Acoutic Labs Audio editor) does it very well but since I have only a few files to fix I don't really want to spend $25..

any way that would be against the code of finding the freeware to do the job. :-)