It looks like I spent about $250 today in my quest for all things Pratchett. I was in error when I said they were all in Kindle format. I had to go to Fictionwise for two of them ... one of which was rather expensive ($13.00 plus for an ebook).
However, when I'm really intrigued by something, I've got to read everything I can about it. And, DiscWorld really intrigues me.