Is is there some sort of library that would allow me to convert a speex file to an mp3 file? If it were do-able from php that would be even better, but really anything would probably work.
If you have gstreamer available on your platform, it can do it for you provided you have the proper codecs installed.
On http://forums.fedoraforum.org/showthread.php?t=61984 I found this piece of code for wma to mp3 conversion, you should be able to craft something similar for your needs:
gst-launch filesrc location=filename.wma ! spider ! lame ! filesink location=filename.mp3