(photo of woman over chair is from the book, "Yoga: The Path to Holistic Health" by B.K.S. Iyengar)
My husband helped me make the chairs at Harmony Yoga: He banged out the backs with a sledge hammer and I filed the sharp edges down from the welding spots. The following Youtube video shows a much less "violent" way of taking the backs out. He uses the same chairs I did -- inexpensive folding chairs from Staples. You can use other folding chairs as well -- maybe you have an old folding chair at home that could be put to good use this way.
It's not a difficult process, but it does take some time to file and sand the edges. The man in the video spray paints the chair back afterward to give a more "finished" appearance to the product.