I have found some really great fabric at Joanne's. I have also found some really thin fabric there. You have to hold it up, feel it and see if it's quilt worth. I won't put anything in a quilt that won't wash and wear well. My quilts are the warm and comfy kind that get washed and dried on a regular basis.
I have also found some really great stuff at Walmart, but again you must be pickey!