First, I was surprised Cakewalk actually charges for an mp3 encoder, which I think should be built it. And then, they rejected 3 credit cards that are perfectly good when I tried to buy it. No problem, I use a free one made by someone else. Not even a real complaint, since the solution was simpler elsewhere, I just find it puzzling

Its quite simple MP3 is a format that is licensed. A fee is required for use. CW passes that fee on to the users if they want to use the MP3 version bundled with Sonar. Pay it once and you need not pay it again for a update.   

There is a lot of confusion about that since there are free mp3 encoders, and h.264 encoders and so on. What people don't realize is that while the software itself can be freely distributed basically for academic purposes and such but if you use them to actually make and distribute stuff you are legally required to pay a license.

you could have used Lame's free MP3 encoder which Sonar gives instructions on how to integrate with it's product.
 
I used Lame for several years with Sonar utl I broke down and purchased it one of those Sonar Versions in the past.

I don't want to sound dismissive, but US $10 is small potatoes in the grand scheme of things- with vsts going $299+: digital age diy music can be fairly expensive... what comes to mind is that scene on the beach in nam "do you want to fight ? or do you want to surf ?"

This topic comes up regularly. You can use the Lame encoder for free or pay the one time twenty buck fee and create MP3 files from within Sonar.

I use the MP3 encoder that comes with Gold Wave, That way I can do batch encoding of a whole album quickly. 
Gold Wave is free to try and real cheap to buy. Highly recommended. You can buy a yearly licence for as low as $15 but a lifetime membership is only $45US - $ 59can  and they supply free updates for life. 
http://www.goldwave.ca/index.php
 
I also use Wave Lab for mastering and they used to include the MP3 encoder but with the new version they now have done the same as Sonar and you have to pay for a licence, so don't just blame Cakewalk.  
It's just so much easier to download something like Goldwave which works without fuss.  Not only MP3 but it also encodes to iTunes plus, FLAC and most all formats. It's also not a bad little wave editor, but I have Wave Lab so haven't dug to deep. 
 
Audacity:  
I don't use it but many do, Audacity also is free and has the LAME encoder but looks like a plug in. 
 
http://www.audacityteam.org/download/
 
Wavosaur: 
And here is yet another free wave editor that comes with Batch conversion for MP3. 
 http://www.wavosaur.com/
 
Not sure how these 3 get around the licence I guess it's because they include LAME which is free. 
So to me $10 is too much when there are free alternatives. 
 
 

LaszloZoltan
I don't want to sound dismissive, but US $10 is small potatoes in the grand scheme of things- with vsts going $299+: digital age diy music can be fairly expensive... what comes to mind is that scene on the beach in nam "do you want to fight ? or do you want to surf ?"

I think people complain because they believe it is free. Like they think Cakewalk could just compile a LAME DLL and include it at no charge. They don't know that MP3 requires licensing. Lots of individuals violate MP3 licensing requirements because they aren't aware they exist. However a company can't or they'll get sued.

dlesaux
This topic comes up regularly. You can use the Lame encoder for free or pay the one time twenty buck fee and create MP3 files from within Sonar.

WHAT ???? 
They jacked the price up ???
Those b*****ds !

LaszloZoltan

dlesaux
This topic comes up regularly. You can use the Lame encoder for free or pay the one time twenty buck fee and create MP3 files from within Sonar.

WHAT ???? 
They jacked the price up ???
Those b*****ds !

My mistake! Its ten bucks. Sorry.