Most people that make their own sleeping equipment usually stick with quilts...no zipper or hood and much easier to sew. Sewing a sleeping bag is a little more entailed, but doable...if you are good at sewing. Of course, adding down makes it more difficult. Do a google search on diy sleeping quilts and you will find a lot of information. You can always use that to make it a sleeping bag.

For buying a bag...I have found that the kelty down bags seem to run a little shorter than advertised. Cost is, of course, relative. You won't find a warm bag that is under 2 lbs that is less than $200. Well, unless it is super clearance, used, or 5 finger discount.