0 degree compact bag on a budget?
I need a bag that's going to keep me warm during cold desert nights, camping on the ground with a tent and maybe a thermarest. I'm told to bring something rated 0 degrees, but 20 may be doable (I've never been out west, so I'm unsure). I'm bringing my mosquito hammock, but it's probably not going to be practical everywhere, but the bag will undoubtedly be used with it too.
I've always bought cheap bags that don't last, being a miserly college student. I really don't know anything about quality bags besides in-store browsing, which all seem to be beyond my price range, or not as compact as I'd want. I'm trying to find something cheap as possible, but still durable and warm. I'm more concerned with warmth and size than weight. I'm not able to get anything top-of-the-line like some of the posts I've seen on the forums.
I have three weeks to prepare for the trip (it was suddenly sprung on me), so there's no time to save money or wait for Craiglist/eBay steals. I've been browsing on Campmor, REI, etc but it's hard to get a grasp on how compact the bags are online.
I apologize for the generic question, I couldn't find a thread that seemed to address what I'm needing, and was recent enough to be relevant.