I dont know all the prices on down bag. I know there are some Chinese ones on amazon. But, im not sure I would want to be cheap on the one thing that will keep me warm at night. Hammock gear makes an econ down quilt that around 160 bucks but you need a war, sleep pad with it. You can pick 2 options out of the 3. Warm, light, cheap.
If you want to save money maybe look at a Marmot Trestle Elite