The full version of Sound Forge used to come with Batch Converter or you could purchase and download Batch Converter separately. I don't know if BC is still available now that Sony bought Sonic Foundry. You might try the Sound Forge forum to see if anybody knows of any updates or where to obtain the old batch converter. You might also try googling for 'batch convert mp3'. I recall seeing a few free/shareware programs that did batch conversion to mp3.
I too use Sound Forge, but do it one at a time when I rip a CD. It's slow going, but at least you can edit the tracks if necessary before converting to mp3.