I haven't seen it in decades (I sold my copy long ago), but if I recall "Karate: The Art of Empty Hand Fighting" by Hidetaka Nishiyama and Richard C. Brown had a section on training methods that included makiwara. Back in 1971 or '72 I made my own makiwara by cutting an eight-foot long 4X4 redwood fence post diagonally along its length and burying 3 feet of it in a rock-lined hole in my back yard. I padded it with a folded towel tied on with a thin line top and bottom. I worked fine, and I never saw a need to buy anything special.
Yours in Budo,
---Brian---