In Quicktime, select all, then drag the small half triangle on left or right to desired position. You can drag either side. Copy, then open a new player, then select Add to paste the copied data into the player. Then save as, make sure you check self contained or you won't save anything. If you can click self contained try moving from one folder to another, then you can go back the the original folder after exiting then save. Make sure you add .mp3 at the end, although it doesn't say that what it is, it will work, I just tested it.
Only problem with this is that you lose the bitrate when you play the file in iTunes, but it still plays. You convert it from the exported mp3 from quicktime back to a MP3 with iTunes by placing the file in a playlist or the library then select convert to mp3. Then it is back to a normal MP3.