I used to make these all the time...pretty much exactly as the post above described.
I would sew in little tabs made from bias tape to run the cording through.
Each bag took 3/8 yard of fabric (watch the direction of any prints!) and about a yard of cording. I used the big cotton cording from the upholstery department, as I found the smaller cording tends to cut into you if there is much weight in the bag.
After the first bag, you will be able to whip them out in 10-15 minutes!