I agree about the spendiness of the BC hardware. It's pretty, but I'm not building a workbench to look at. So I'm using a Shop Fox bench screw (about $30) both for the wagon vise and a leg vise on my bench.
I built something similar around 1990 when I was a really poor grad student, using 1" threaded rod and a dog block made of a chunk of walnut from a tree we had to take down in the back yard. I just made the block with "ears" that fit into dados in the vise slot - all with a hand saw, a plane, a brace and bit, and one 3/4" chisel, since I had no money for anything else. It worked pretty well for years, even with a very humid environment (a cellar in Kentucky). It did have a tendency to ride up a bit as you tightened the vise. I just got used to giving the dogs a little tap after tightening to make sure the workpiece was fully seated to the workbench top.
This time I'm building to much the same plan, except I intend to use angle iron to create a channel for the "ears," now also made of angle iron. In other words, a short piece of angle will be bolted to either side of the block in a shallow dado, and four longer pieces will be attached to the front and back of the vise slot (two on each side of the block) to in effect create a lining for the dados. Hard to describe, easier to see, I hope!
One downside to this approach is that it makes the vise slot pretty wide (3") because the dog block has to accommodate both the dog hole and the screw. But I'm not comfortable with setting the screw further into the bench, so as to make the slot narrower - I figure it's better to keep the force of the screw as close to directly behind the dog as possible. If you're using high-tolerance machined parts like BC, I suppose having the dog hole an inch or two away from the screw is ok. But with this cheaper model, it would probably make the block rack counter-clockwise.
Anyway, total investment so far: 2 bench screws, $60; one 6' piece of 3/4" angle iron, $8; a little block of walnut, free from the scrap pile of my hardwood supplier.
I'd appreciate any suggestions!
Miles