The guys that created this kit are responsible for the article that has gotten the most traffic on the main TSM site;
http://twostrokemotocross.com/2010/04/new-2011-yz125-spy-photos/Yes it may be high-priced, but it's not outrageous for what you get. A custom gas tank is big bucks to manufacture, plus the custom sub frame. This is all done by a small shop and has nothing to do with Yamaha motor company.
It's really funny but the biggest reason that many people didn't want to buy the new Yamaha 2 strokes was the fact that the plastics looked dated! To me that's the dumbest thing ever, but hey each to their own.
One thing is for sure, if you show up with your Yamaha two stroke with that kit, you will get a lot of attention.