Ray Jardine still sells his quilt kit on his web site (rayjardine.com). The most basic one is $89, and that's a warm-weather only version. I guess the question is how low the temperature might go where and when you're using it.

The common synthetic insulations found at Fabric Depot, etc. are too heavy and not compressible enough to make a satisfactory bag or quilt.

I wouldn't completely dismiss the idea of harvesting down from an old bag, jackets, etc. It won't be the lightest or the best, but could be adequate and cheap, especially if making a relatively thin, sewn-through quilt. If you're using baffled construction, there's so much work involved you might as well spend the money on good insulation if possible. You can, if you have some time on your hands, "grade" the down by hand, removing all the little pinfeathers. I've actually done this, and it was quite a chore, but it worked.

I made a down bag using "floor down" from Feathered Friends, which is the down they vacuum up after a day of making bags. It has to be washed, and it contained a few bits of assorted debris. If I were doing it again, I'd just spring for the good stuff and avoid the hassle, but the point is it worked.
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Always remember that you are absolutely unique, just like everybody else. -Margaret Mead