Think the pair pictured was ~$125. I mean, they're just made of aluminum and require basic CAD shit (I think he said it took him under an hour of work), there's really not a lot of cost other than finding a willing fabricator. I had originally envisioned this as a super small business venture since Kirkham doesn't appear interested in making these at all.
The problem being that, for most fabricators, this isn't really worth their while unless I wanted to make like 100+ at a time or something. I think there's a better design here that I alluded to (and you sort of did wrt adjustable handle position on the SSB), basically make the end handle adjustable as well so you could adjust the distance the handle is from the bar. That'd give it a whole lot of flexibility in terms of body size etc. But yah, since it's so small potatoes, I've had trouble getting anybody to bite on making a small batch of these for me.