Lamina™ 15F/-9C

My Mountain Hardware Ultralamina 15 is 3 lbs and I have used it comfortably below 30. Maybe you can find one used for that price, as bags like mine are 12+ years old now.

If you can find a Mountain Hardware Lamina -9c that's a pretty good option that's often on sale. Big Agnes has some pretty good womens bags. Buying used also a good option to make your money go further unless you have hangups. I would much rather have good used gear than the Coleman / Decathlon garbage people push on this sub.

I think you have a valid concern. The problem is not the danger of dunking your bag in a creek, or getting it rained on, it is night after night of absorbing the moisture evaporating from your body, when there is no opportunity to dry it out. I had this happen to me in Oregon, my down bag completely collapsed and it made for a cold night. After that I bought a Lamina, which is fine but it's not as warm and heavier. If I were buying today, I would probably get a down bag with the Nikwax treated down, which supposedly is moisture resistant. I recently bought a Rab parka treated that way, but haven't really used it in wet conditions yet.

For posterity, the sizing is indeed important.  The non goretex versions are "performance mummy cut" which mean these are smaller.  The goretex ones are the ones you bring for expeditions, these are the big bullet proof tankers known as "Expedition mummy cut".   Inside the Expedition Cut, you can gear up with your belay down jacket and stuff, theres more room and then you can get a -18c instead of a -40c for example. The beefier goretex expedition one is interesting if you sleep straight outside in winter, with no tent.  It stop wind and melting snow wont wet the sleeping bag.   For serious winter stuff you can add a VBL in that melting pot of kit to manage humidity and dew point but its not in the main subject. Things to remember: - Performance cut; - Expedition cut. I personally have the blue and red MHW -40c goretex, the -18c, the -18c goretex and the -9c. Each sleeping bag have its particular usage in my activities.