Why not look at data provided at some websites?
The pictures below are form the Dutch website Tweakers.net.
It gives you a good overview of what happens over time.
Here is the K20D + kitlens for the Dutch market (in €):
And here is the K-7 + kitlens:
And the K-x body:
You can see that the K20D started out around €1050, now €697, while the K-7 started off around €1200, now €927.
When the K-7 was released (Aug 09), there was no big price fall for the K20D before or after the introduction!
However, the K20D price had allready dropped gradually over time to € 697 and stayed more or less stable since then.
Be aware that these graphs show the *lowest* prices available on the internet for the Dutch market and the "gemiddelde" (average).
It may very well be that average street prices have dropped much more around the K-7 introduction.
I expect you will see the same effects for the new camera's to come.
Based upon that assumption, the lowest K-7 prices now will not change that much, while a new high end model will start at €1300 (1200+some devaluation).
Conclusion, if you are looking to buy a new K20D or K-7 now, just buy it. You might as well enjoy the camera today.
Waiting untill new models arrive will not impact price that much.
Cheers, Bert