Sales are up right now on The Clymb for a bunch of the Sierra Designs down bags, most at ~60-70% off, meaning there are down bags for a range of temps at prices from $85-$200.
In particular, the Sierra Designs Cloud bag received a pretty good review here a while back--biggest problem was the list price. However, at $200, it's pretty amazing for a ~28 oz 15 degree bag.
Full disclosure: The Clymb is one of the many membership gear sites where they give me some account credit if you sign up through my account link and eventually make a purchase. I'm not trying to get you to buy anything -- I only post when I see an exceptional deal on something that fits the ultralight ethos.
That said, if you decide to sign up, you've got my thanks -- I try to use account credit to buy gear for friends to get them started on hiking. Free credit seems like it should go to grow the hiking community. Here's the link: http://www.theclymb.com/invite-from/TimHaynes