Been there and done that. I am WAY over on the low cost side of things.
I went though the same "AHA!!" moment when I saw the low $ quilts advertised. The people here pointed out the cotton and also predicted that the "down" would be mostly feathers instead of mostly down. Your quilts list 550 fill, which is not too bad.
I also hiked once with cotton. It rained. I was home a day or two before the dang pants dried out and I warmed up.
When you get all done with a cheap sleeping bag system and get to the Pack it up and load it on your back part, things go to hell in a hurry. Quite simply, the volume becomes impossible to load. That's what happened to me last year with version one.
I wound up with a gearskin type pack (homemade). It uses a blue closed cell pad as the frame. I made a two layer hammock. ( see Risk's Zhammock)The pad fits between the hammock layers. This gets rid of most of the complaints about sleeping on a pad in a hammock. (which are true, if you sleep right on top of the pad)
I got a 50 degree bag from Sportsman's guide. I supplement it with a poncho liner when needed. This has gotten me to 40 degrees or so. All my clothes and rain gear will get me through lower if I ever get caught.
So, I'm down to a 12 pound base weight for sleep and pack weight, without breaking the bank.
My entire pack weight will be around 25 pounds this year, with 4 days food.
You're on the right track. Just keep an eye on the whole hiking system.
Miles of Smiles