I agree that one's sleeping bag is critical gear that needs to be entirely reliable. It ranks right up there with footwear and shelter as the items that really must do their job correctly. Buying a used sleeping bag is one way to go, but has some risks if the bag has not been well cared for.
If I were buying a new bag and needed to watch every dollar I spent I think the best place to economize is not to buy from a manufacturer with no track record, especially from China. Chinese manufacturers often are just blindly copying someone else's design using cheaper materials, but they have no idea why a cheaper material may not be functional, because they don't really understand what its function is. Instead, I'd go with a reputable maker who understands what backpacking is, and I'd economize on the fill power of the down. 600 or 650 fill power bags may be slightly heavier for the same amount of loft, but they are significantly cheaper than 800 or 900 fill power.
In the past I'd have recommended REI without hesitation as a good mid-price brand with acceptable quality. I haven't been as impressed with their down-filled sleeping bag offerings lately when I've looked at them. I'd still look there, though. Kelty is no longer a premium brand, but it is not yet an unreliable one. They also might be a place to look. For a used bag, I'd be pretty confident buying a Western Mountaineering or Feathered Friends bag.
Edited by aimless (12/06/17 03:05 PM)
Edit Reason: added a sentance & expanded another