One idea is the "Warm Window" products. They sell a 4 layered quilted, insulated fabric and the hardware to hang it. Here is there main info:
http://www.warmcompany.com/wwpage.html
You can also buy the fabric at most larger fabric stores and on line.
So, your budget is more like $20 a window? See what this frugal person did with only $20:
http://countrylife.lehmans.com/2007/...window-quilts/
Another frugal minded person did this:
http://energyboomer.typepad.com/ener...-make-ene.html
One of my favorites, probably because hers LOOK like quilts:
http://www.manytracks.com/Homesteading/winquilt.htm
Hope some of those ideas work for you and others. I've just used a thick batting on my two sewing room windows for the last several years. I hang lined curtains in front of it, then I can take the top part down half way to let more light in if I want.