This is where I would use the least expensive fabrics I have and buy a 25 lb. bag of rice and a smaller amount of flax and lavender. The latter 2 need very little in each. The last time I did them (about 10 years ago) I sold them for $7. You should be able to get 10 (maybe less). If you really want to sell a great deal. To make a hit of it I kept a small microwave so I could demo them. I sold 40 of them as well as many that were just plain rice. The bags only have to be little more than half filled. You will make a profit but maybe not as much as you may be thinking for all your work. Just keep in mind why you are doing this project.