Get a sheet at the thrift store or Big Box store of the colour you desire, throw it in the washer, splash some bleach randomly on it (if you like that look), wash, remove, wad it up and let it dry.
I am offering up the suggestion, look for Quilting supplies. Cloth from the "fabric store" is about 60 inches at most. Cloth from quilting supply can be twice that with. You can have the backdrop 8 to 10 feet by however many yards you wish to purchase. Make your own backdrops?