For those wishing to make their own jong, the tapered arms are not too difficult to make. If you want them custom made anyone with a lathe can turn them in a matter of minutes. If you are aiming for a budget dummy as per the poly pipe option, pop into your local DIY store and look at the table legs, they normally offer a nice tapered range that can be secured through the body of the dummy with threaded bar.
I was able to build my own from 8.5 inch diameter PVC (6 ft). 2 sections of 4ft. dowel (2inch) then for the leg i used pine. and mounted it on oversize L brackets per recommendation of my Sihing. I used a power sander to fine tune the arms and then mounted the PVC on the L brackets after cutting out the appropriate holes based on the design specs I found online. For my first one it turned out pretty good. Building your own is so much cheaper than buying in most respects.