Ledge Sports Techlite -20 degree F sleeping bag $60
Product information: http://ledgesports.com/product/techlite-20/
This is a synthetic bag meant for cold temperatures and expedition mountaineering/canyoneering/adventuring. Works when damp even in freezing conditions. I've only used it a couple times. Rated to -20F/-28C but I have only used it down to 0F/-18c in snow in the Cascades so I cannot confirm its comfort rating.
Warranty application: http://ledgesports.com/warranty/