I've made grow bags with the black landscape fabric. Buy a roll of the wider size, double it over and sew it along the edge. Measure off how tall you want them to be, remembering to add the radius of the bag. Then tie with some good cordage and cut below the knot. Turn inside out and you have a cheap ass grow bag.
I use lava rocks in my soil mix. Also try to add lots of leaves, grass or other mulch around the plants.