I use Gold Wave, it's not exactly free but you can use it forever for free. I keep meaning to send them the $50 for lifetime as I feel guilty,,, sometimes about this... But It has the batch converter so I can convert a whole album in one fell swoop. That's about all I use it for.
I would never export directly to an MP3 as then I would be skipping an important step,,, Mastering which I do in Wave Lab.
But as said, MP3 encoding is now free in the free version of Cakewalk so forget X3 ( I did)