Uniqlo in NYC has these down ultra-light jackets that weigh 7 ounces. They also only cost $79.90 + tax. I think this is a very affordable option and has comparable weight to the patagonia ultra-light down sweaters at a much cheaper price.
I also love Uniqlo's heat-tech long-john underwear for layering. They are super light and very warm.
For those of you who don't live in NYC or in Tokyo, Japan, you may be able to get them to ship the jacket to you by calling them. Heres more information on the product: http://www.uniqlo.com/us/CPaGoods/itemcode=069087#top

