bitflipper, yes I did purchase this and got it for under $50 (maybe I never actually said that in my original post).  In the last email exchange I had with TruePianos (asking if I should discuss this deal on the Sonar forum), it was replied to me, and I quote, "The discount is valid for owners of any CakeWalk VST host software." 
Since the above does not seem too particular about the Sonar version, I can only hope there were no misunderstandings lost in translation (the responder admitted he is not a native-English speaker).  All I can say is, if you meet the definition above and are interested in TruePianos at that price, contact them and see what they say.  If the price does not interest you, or if you are concerned about sharing your Cakewalk serials, I am not trying to convince you otherwise.  I just wanted to share what I thought was an interesting deal. 
 
EDIT:  I received another email from TruePianos (I think he is monitoring this thread now), and he clarified there was no misunderstanding.  He said they would honor a discount from any Cakewalk serial number product that hosts VST, for example he said, even "Cakewalk Home Studio 2004".  Regarding serial number concerns, he states that they need it to inject the serial into a Cakewalk installation DLL to determine validity and discount eligibility.  I think I've done my diligence by sharing this offer, so I don't plan to keep posting... but I wanted to pass on the accurate info as it was conveyed to me.  Again, if it interests you, contact them.  Truepianos has been very responsive to my inquiry.  Good luck.

Sorry I was unaware that the version we have is not a good example. 
And good point about it being a light load VST, sometimes that is needed. 
 
 
 

48 dollars for 5 true pianos... to my ears they sound good

Yes, bought the full version some years ago now when they were on special. Not sure what price that was at the time, but TP is my go to piano for roughing out new songs as the CPU hit is very light and the better pianos in the full version really do sound good.

I also have full version, if I remember correctly I have payed more then $50, but not 2 times more.
 
"Old" is not always bad. TruePiano has old serial number authorization. And it works on any Windows (including Wine in Linux).
 
I like the sound. I rarely play Amber, but from other I do not have particular favorite.
 
I am a noob, but I tend to disagree about using it in a big mix. TruePiano is not so good in mono mode and has too many "side" sounds. Pianoteq "fits" into mix faster. But Pianoteq, like Roland DPs, is pure algorithmic and sounds artificial for me. Big sample based creatures tend to produce fancy sounding effects (samples mixed within an engine are not the same as sounds mixed withing a real instrument). So I prefer "hybrid" solutions, like TruePiano and Kawai DPs.

I'm slowly getting GAS here people....

I found this offer a few days ago and used my X2 serial number, I think.  I went looking for the site and saw the upgrade page mentioned on google.  I didn't think it would still work, after all this time, but tried several serial numbers until it did.
 
It is well worth it - I use it a lot, and the other five pianos are really nice.  I have some big sample library pianos, but use this more as it is so light on the system and sits well in a mix.

Even though I have Kontakt Komplete I grabbed this for $48.  Bitflipper is correct about the footprint, this is a light-weight way to get reasonable piano sounds for fitting in the mix somewhere. 
 
My SPLAT serial number worked, so maybe they fixed the issues.  If you had a problem with your CSPT-X.XX format serial number maybe give it a try again.