Of course, there's always the great outdoors! Both of these were taken in my yard somewhere. The key to shooting outside is to shoot on a more overcast day. Contrary to what you might think, bright sunlight is not good because it causes harsh shadows (like in the first picture). The second was taken on an overcast day.
A baby blanket! The background in these pictures is simply a baby blanket taped to the wall!
A bed sheet! These backgrounds are a flat bed sheet taped to the wall!
Both of these were taken close up on a couch!
I've got a few more cheap backgrounds to share but we'll save those for another post :) My girls are getting into trouble and I must go....
What have you done for a cheap background for your photos? I'd love to know!