Two things,
1. Here is a plan for the cheapest version you could make. The wallmart idea was brilliant, I would have paid 3x as much for just the fleece. http://www.backpacking.net/makegear/liner-quilt/index.html

2. Rather then get extra geared up, couldn't you just sleep dressed? I did it in my 30f Big Agnes bag at 5f, I was toasty! I would just wear my next days clothes to bed, and since they are clean you have no worries. I also can't stress enough that you will be 100x warmer when your head, feet, hands, and wrists are warm. Those places are where you lose the most heat. (Those wrist bands are a must!!!!! I even wear them when hiking or climbing. I can go sleeveless and as long as I have the wristbands on, I'm warm. Maybe it's psychosomatic but I swear it works, not a little either. That night I spent dressed I got over heated in the bag and just took off the wristbands. It cooled me so muc I had to out them back on an hour later.)

Best of luck.
[color:"green"] GuruJ [/color]