Synthetic quilts are easy to sew and pretty cheap. Check out kits at RayWay products, or purchase the materials yourself at e.g. Outdoor Wilderness Fabrics. It just takes a few hours cutting and sewing time to whip one out, I've made three so far, and more are coming. Plans are not too hard to find, and the exact design is not critical.
And they are even cheaper if you can find a closeout on lightweight uncoated nylon or synthetic insulation.