"To actually compare apples to apples you have to compare the exact same regulator body I'm using. I use Cornelius regulators. I think you will find they are a bit more than $40. Also if you buy from several different places you have to total the shipping and handling charges."
So that answers my question about why the brewery regulator costs much less: here a Cornelius body costs $50, and that's without the dual pressure gauges.