This is a little below the level of quality most of you are talking about, but I just bought a down bag for this temp range at a great price. It's a SlumberJack Denali Summit II, it's rated to 5 degrees (soft rating probably), weighs 3lbs, and is very compressible. I was a little hesitant of the brandname at first, but I am very happy with it and it was only $127 US, including S&H, from Campmor.com.
If you are looking to save cash and still have a decent bag it's not a bad option.