I was doing some updating on the church computer today and noticed that the sermon audio files were starting to add up and they were all wav files. That's how I normally export the sermons with Audacity, but I need to stop lol, it just takes up too much space. Anyway I found this really cool program online that will batch convert multiple files. I did 19 wav files at once. It's not extremely fast but it gets the job done. You just drag and drop into the exe file.
http://www.rarewares.org/mp3-lamedrop.php