Light, cheap, durable, compressible and warm is an impossible combination. You will have to decide which one to give up.

I have an Alpine Design 20 degree bag. You can get the women's bag which is the same color as the men's for $39.97. The men's bag is $59.97.

You can also buy them at Sports Authority. I would avoid any other type of bag they have there.

It weighs 2.5 pounds including the stuff sack. It keeps me warm to the mid 20's without a pad. I do wear a base layer in the bag.

The thing you are giving up is compressibility, but it isn't a major problem compared to a more expensive Sierra Design bag I was given. Instead of the stuff sack, you can put it in a plastic bag and stuff it in the bottom of your pack. Leave the top of the bag open to let the air out. If you are putting other things over it, it's not likely it will get wet.

I'm into my fourth year with the men's bag. Durability is not an issue. I've slept out in it about 100 nights.