I also think your cheapest approach( that would really get the job done) would be CCF pads and a Speer SPE ( or make one). Stack torso segments pretty thick, less so under your legs. Next in expense will be the SS, and then down UQs.
If y'all can do minus 13*F in a basic SS, I wonder how much CCF you would need? Maybe not all that much.
For I consider that the sufferings of this present time are not worthy to be compared with the glory that is to be revealed to us....that the creation itself also will be set free from its slavery to corruption into the freedom of the glory of the children of God. For we know that the whole creation groans and suffers the pains of childbirth together until now.