Hi sassy,
greetings from the north central valley of CA.
I usually get the backing material from the sales rack or when I have a coupon. There are some threads on the QB about inexpensive backing fabric. Some quilters like to use flat sheets (I am not one of them). As far as batting.....use a coupon at the fabric store. Some quilters have discussed using old blankets as fillers. (I would not try that for my first free-motion quilt)
Have fun.....and if you can't finish this one, get scrap happy on another top. Then you'll be a quilter with a UFO.