I fell in love with Melodyne!  Last night I activated my free 30 day trial from Essential to Editor.  Does anyone know if Sonar has a special deal on the upgrade for X3 users?
 

Celemony has been very responsive to SONAR customers and had a deal to upgrade for $149 for 10 days after registering Essential.
 
I would suggest emailing and letting them know your situation and ask if you can still get that deal from them... after all, it is almost Christmas!
 
Edit: Had to check the upgrade price for X3 users. It was 149 (Euros/USD). The email was sent as X3 users registered Essential and "expired" in 10 days, but I have heard of a few who wrote them directly.

I am hoping Celemony will let me upgrade to Editor also.  I missed the email and then upgraded to Assistant for same price they offered Editor.  Waiting to hear their response....

Ok nchardy and olemon : Keep us up to date !
At the end of November/beginning of December, Cakewalk offered an interesting upgrade bundle Sonar x3 with Melodyne editor (from sonar X2 producer) for around 269 € (I don't know exactly). I missed the deal, and Cakewalk answered me there could be another special offer but not 100% sure.

i missed the upgrade the first time.  i wrote to them tonight at 8pm and within a half hour they upgraded me to the editor version at the discounted price.  give it a shot....

Got it!  I had to email a copy of the invoice which showed when I bought the upgrade to Assistant.  Celemony sent me an Editor serial number, downloaded the installer and good to go. 

Very nice :) Celemony has been good the X3 folks!

I would imagine this was a good quarter for Celemony too.

I found Melodyne Editor to be excellent (I've had various versions of Melodyne before it started shipping in Sonar so I just needed to download the latest Melodyne varsion).
 
I recorded a friend's guitar part but there was one chord that had one note that was muted too soon accidentally. Opened it in Melodyne and it automatically detected all notes using its polyphony detection algorithm. It was trivial to adjust the length of different notes within the chord with excellent results. He is a pretty old-school guitar player and would have noticed artifacts but said that if he didn't see me do it he would not have known that anything was changed.
 
So for me at least the Editor version was worth it.
 
EDIT: I'm glad Melodyne is well integrated into Sonar now. That was one thing I didn't like about the way it used to work. It used to be clunky but ARA made it seamless. Only thing I would change is to have more controll over vibratos and freehand pitch drawing like in V-Vocal.

I just emailed Melodyne,  I'll wait and see if they give me a discount on the upgrade..