I bought the smallest one from this site:
http://sewingmates.com/Order_Here.htm
I really wanted the larger one, but couldn't afford it. This works pretty well for my needs. What's good is that you can configure it for multiple machines, rather than purchasing one for each machine. I also made myself a raised platform on the idea of what others have with foam, but I used cardboard boxes (couldn't find thick enough foam w/o buying multiple pieces).