Compact cold weather sleeping bag on budget**
No such thing
Yep. A big fluffy bag will never be compact or cheap. A true cold weather bag 20º or 0º is a specialty item. You can keep an eye out for used, or just carry 2 (or 3) lighter bags.
** Reminds me of working in retail; The customer, often 1 or more a day, would ask for a a pack thats:
1. great for a weekend
2. also for an extended trips
3. and a trip to Europe
4. lightweight
5. cheap
6. In purple