Check out the KAQ Lost River at arrowheadequipment.webs.com. I've used it to 30* and it worked great. It's on sale for 110.00. I got it when it was 85.00 but I don't know if that sale will come again anytime soon.
It is only a 2/3 uq so you would need to supplement your feet but at only 16-17oz, it is a great uq for the weight. I use 6 panels from a zrest as my padding for my pack but even when I didn't it was worth it. Just a thought.