Sierra Trading post got in the Vaude Ice Peak 150 35 degree rated 650 FP down bag that got a Backpacker Review Vaude Ice Peak 150 2010 Backpacker Magazine editor's choice.
http://www.backpacker.com/gear-guide-apr...-bag/gear/13913

Seeing the bag's wonderful 18 ounce weight, I almost pulled the trigger with a 40% off $150 coupon yesterday, but then noticed in reviews that it is a snug fig for bigger folks. At 225 lbs, I suspect it would be too snug for me.

This bag doesn't quite meet your 20 degree requirement, but if you are on STP's email list for their coupons, you can pick up the bag for around $100 or less and have a lot of money left from your budget to add a vapor barrier/liner for colder weather.

-Matt-