There are a ton of great options these days. I'd echo the sentiment of fronting a little more money up front to get one that will last you years, and will assure you comfort when you start approaching the temperature rating. With that said, you can find a pretty solid bag that will get you close to 20 degrees, under 3lbs, for around $300... Sea to Summit is fairly new to the game, but I own one of their bags, and their recent Ascent series has great reviews. If that's too rich for you, take a look at the Kelty Cosmic Down 20... I still own and older version one that I bought years ago, and have held onto it for a loaner bag for friends. It's about 2.5lb, packs fairly small, comfortable sizing, and can be found for $100 if you dig around and are patient.