I did a queen on a Brother XL2600. That's one of those cheap $100 Wal-mart machines with a 4.5 inch throat. Lots of the ladies on here have machines like that. You can get it done.
I now have a Brother PQ1500S which has a 9 inch throat. I can twirl a queen 180 degrees in it if I need too and I'm not a very good quilter. I think so of the ladies on here could quilt a circus tent in it.