I lucked out and my neighbor gave me a 20ft long piece of 5/8" solid steel bar. That's what the boring bar, and backrest, and the stabilizer bar are made from. The very base is made from (this was nice) a spike strip that someone put in their driveway back when I used to read power meters around here.
It is 1/2" x 3" or so plate, and had 4" x 1/4" spikes welded on them. It got 3 of my tires, and thank goodness that after 10 years I learned to carry a box of plugs with me. 7 plugs later, I finished my route, with the strips in the back of the truck cause NO ONE would have believed that story, haha.
Anyway, so that's the base. The stem of the backrest is adjustable for whatever reason on mine. Just a couple pieces of an old jackstand.
The backrest bars just have a couple of 1/4" bolts, with adjustment nuts on there, for a different boring bar I'm building out of an old weight bench bar at 1" diameter.
The tool holder was from a handle for a drill press, cut in half and ground down. The bit holder was a sliver of the 5/8" bar, rounded off with a slot ground into one side to hold the bit securely (why didn't i just use my sorby tip, duh?)
Tried it out on some sassafras endgrain, and it was wonderful. The control, and complete lack of effort are phenomenal. I should have made one out of wood looong ago had I known that it was this much easier.
Oh yeah, total cost was about 4 bucks, but only cause I bought a couple extra bags of bolts. It now needs to be sanded and all the non metal to metal contact surfaces painted. A little more dressing up some rough edges with the grinder wouldn't hurt either.