I can't remember which thread mentioned it, but someone said that Menard's sells a crate with wheels, so I went to the Menard's in Rice Lake, WI today to check it out. And I scored one! For $20. It is a Rubbermaid product, and my little Viking 5610 fits in it perfectly, with lots of room left over for everything else, including my laptop, which I take to my Guild's business meetings (having wimped out last August and agreed to be BOTH sec'y and treasurer this year).
One pic shows the outside of the box, if you decide to look for this, the other shows it opened up, with the pulling handle extended.
Hope this helps somebody else!