A company called JSD products, sells a version they created as well - same theory
http://www.jsdproducts.com/
Like Tophog mentioned it seems like a hefty profit for them but hell...it's a highly demanded part, that works great and many people just don't have the know-how or time to make their own. Many people would rather just spend the 40$ to ensure they are getting a working part, and save the time.
Yes, it is awesome for those of us who can take the time, to do this stuff ourselves, but you cannot blame companies for charging 40$ for one either really