How about Konqueror. Open the directory with the wavs, highlight what you want, select 'Open With' then enter
mpg123 <Desired Options>
and it will convert all the files.
I don't use MP3, so the encoder name above might not be right? I am now an ogg man, but I simply 'Open' groups of wavs with oggenc, or to convert back to wavs, oggdec.