I forked out the $20 as well. It's worked great for me too.

It's been suggested umpteen times but for some reason the moderators won't do this, but here it is again:  MAKE THIS LINK A STICKY:
 http://www.thirdtake.com/2007/11/15/sonar-mp3-encoding-with-lame/
The same query comes up almost weekly.  LAME IS FREE AND IT TAKES ONLY A COUPLE OF MINUTES TO DOWNLOAD IT AND CONFIGURE IT TO WORK WITHIN SONAR.  YOU DON'T NEED TO SPRING FOR $20 OR USE ANY ADDITIONAL APPLICATION.

I've tried out the utility indicated by wruess now, it's excellent.
 
No hassle no fuss lame encoder setup, brilliant!

Hmm, having said the above, the resultant mp3 is horribly, horribly compressed.  Like quiet sections louder than loud sections horribly compressed.  
 
I'm going to export (or rather, record) to a wave file first then convert to mp3 to try to figure out where the problem lies.
 
[edit] It was the UMPlayer that I was using the play back the mp3 file; it really makes a mess of mp3 files for some reason, producing horrible audio compression.  I guess its rendering engine isn't the best!  Windows media player makes a much better job of it.

Funkybot

daveny5
I can't believe people will pay $400 for Sonar, but then whine about forking out $20 for the MP3 encoder.

I can't believe people pay $400 for Sonar, and it doesn't already come with an MP3 encoder.
 
Please let me know which other DAW's charge for this functionality.

Cubase charge £12 GBP for their MP3 upgrade.
Protools £9.95
Presonus 'Free' and 'Artist' have no MP3 support at all.

Is it poor practice to just use iTunes to convert your .wav to a .mp3?  It's a solid converter, but it does add an extra step in your workflow as opposed to the $20 Cake option.  I'm sure you have iTunes on your machine or another machine.
 

I didn't see this one listed, the Freemake Audio Converter is excellent for MP3 conversion.  It's also a great tool for ripping samples from YouTube-like videos of various formats.  It's also free:
 
http://www.freemake.com/free_audio_converter/