Even without a sewing machine (by the way, if you run across the term "thread injector" here on the boards, that's a sewing machine), you can still make an underquilt out of an old poncho liner. Dejoha has wonderfully-illustrated instructions located here
. I've, personally, successfully used one down to 41 F
after some adjustments.
As long as you can get your hands on a poncho liner, 1/8" shock cord, some cord locks, something to help you run the cord through the hems, and a lot of patience, you're good to go.
Total investment was probably in the $30 range. It's not light compared to other options out there, and it sure doesn't compress. On the other hand, it's hard to beat that price.
If you've got any questions about it, let me know!